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topological sorting
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‎src/com/blankj/hard/_329/Solution.kt

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package com.blankj.hard._329
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import com.blankj.ext.print
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import com.blankj.structure.MultiDimensionArray
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import kotlin.math.max
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class Solution {
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fun longestIncreasingPath(matrix: Array<IntArray>): Int {
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if (matrix.isEmpty() || matrix[0].isEmpty()) return 0
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val lengths = Array(matrix.size) { IntArray(matrix[0].size) }
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var res = Int.MIN_VALUE
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for (i in matrix.indices) {
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for (j in matrix[0].indices) {
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val length = dfs(matrix, i, j, lengths)
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res = max(res, length)
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}
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}
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return res
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}
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private fun dfs(
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matrix: Array<IntArray>,
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i: Int, j: Int,
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lengths: Array<IntArray>
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): Int {
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if (lengths[i][j] > 0) return lengths[i][j]
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val dirs = arrayOf(intArrayOf(0, 1), intArrayOf(1, 0), intArrayOf(-1, 0), intArrayOf(0, -1))
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var length = 1
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for (dir in dirs) {
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val row = i + dir[0]
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val col = j + dir[1]
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if (row in matrix.indices && col in matrix[0].indices
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&& matrix[row][col] > matrix[i][j]) {
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val path = dfs(matrix, row, col, lengths)
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length = max(path + 1, length)
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}
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}
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lengths[i][j] = length
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return lengths[i][j]
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}
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}
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fun main() {
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Solution().longestIncreasingPath(
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MultiDimensionArray.createTestData(
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"[[1]]"
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)
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).print()
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Solution().longestIncreasingPath(
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arrayOf(
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intArrayOf(9,9,4),
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intArrayOf(6,6,8),
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intArrayOf(2,1,1),
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)
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).print()
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Solution().longestIncreasingPath(
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MultiDimensionArray.createTestData(
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"[[3,4,5],[3,2,6],[2,2,1]]"
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)
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).print()
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}

‎src/com/blankj/medium/_207/Solution.kt

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package com.blankj.medium._207
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import com.blankj.ext.print
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import com.blankj.structure.MultiDimensionArray
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class Solution {
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fun canFinish(numCourses: Int, prerequisites: Array<IntArray>): Boolean {
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if (numCourses <= 0) return false
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val inDegree = IntArray(numCourses)
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for (prerequisite in prerequisites) {
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inDegree[prerequisite[0]]++
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}
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val queue = ArrayDeque<Int>()
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queue.addAll(inDegree.indices.filter { inDegree[it] == 0 })
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var res = 0
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while (queue.isNotEmpty()) {
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res++
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val curElement = queue.removeFirst()
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for (prerequisite in prerequisites) {
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if (prerequisite[1] == curElement) {
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inDegree[prerequisite[0]]--
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if (inDegree[prerequisite[0]] == 0) queue.add(prerequisite[0])
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}
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}
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}
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return res == numCourses
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}
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}
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fun main() {
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Solution().canFinish(
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2, arrayOf(
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intArrayOf(1, 0)
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)
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).print()
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Solution().canFinish(
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4, arrayOf(
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intArrayOf(1, 0),
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intArrayOf(2, 0),
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intArrayOf(3, 1),
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intArrayOf(3, 2)
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)
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).print()
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Solution().canFinish(
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1, arrayOf(
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)
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).print()
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Solution().canFinish(
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2,
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MultiDimensionArray.createTestData("[[1,0],[0,1]]")
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).print()
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}

‎src/com/blankj/medium/_269/Solution.kt

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package com.blankj.medium._269
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import com.blankj.ext.print
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class Solution {
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fun alienOrder(words: Array<String>): String {
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if (words.isEmpty()) return ""
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// graph stores outDegree's chars(value) of char(key)
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val graph = mutableMapOf<Char, MutableSet<Char>>()
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val inDegrees = mutableMapOf<Char, Int>()
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for (word in words) {
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for (c in word.toCharArray()) {
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graph.putIfAbsent(c, mutableSetOf())
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inDegrees.putIfAbsent(c, 0)
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}
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}
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for (i in 1 until words.size) {
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val w1 = words[i - 1]
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val w2 = words[i]
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if (w1.startsWith(w2) && w1 != w2) return ""
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var j = 0
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while (j < w1.length && j < w2.length) {
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val c1 = w1[j]
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val c2 = w2[j]
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if (c1 != c2) {
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if (!graph[c1]!!.contains(c2)) {
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graph[c1]!!.add(c2)
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inDegrees[c2] = inDegrees[c2]!! + 1
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}
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break
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}
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j++
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}
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}
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val queue = ArrayDeque<Char>()
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queue.addAll(inDegrees.keys.filter { inDegrees[it] == 0 })
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val builder = StringBuilder()
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while (queue.isNotEmpty()) {
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val ch = queue.removeFirst()
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builder.append(ch)
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for (neighbor in graph[ch]!!) {
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inDegrees[neighbor] = inDegrees[neighbor]!! - 1
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if (inDegrees[neighbor] == 0) {
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queue.add(neighbor)
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}
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}
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}
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return if (builder.length == graph.size) builder.toString() else ""
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}
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}
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fun main() {
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Solution().alienOrder(arrayOf("wrt","wrf","er","ett","rftt")).print()
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}

‎src/com/blankj/medium/_444/Solution.kt

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package com.blankj.medium._444
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import com.blankj.ext.print
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class Solution {
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fun sequenceReconstruction(nums: IntArray, sequences: List<List<Int>>): Boolean {
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if (nums.isEmpty() && sequences.isEmpty()) return true
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if (nums.isEmpty() || sequences.isEmpty()) return false
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val graph = mutableMapOf<Int, MutableSet<Int>>()
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val inDegrees = mutableMapOf<Int, Int>()
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for (seq in sequences) {
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for (num in seq) {
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if (num < 1 || num > nums.size) {
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return false
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}
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graph.putIfAbsent(num, mutableSetOf())
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inDegrees.putIfAbsent(num, 0)
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}
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constructDirectedGraph(seq, graph, inDegrees)
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}
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val queue = ArrayDeque<Int>()
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queue.addAll(inDegrees.keys.filter { inDegrees[it] == 0 })
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val res = mutableListOf<Int>()
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while (queue.size == 1) {
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val num = queue.removeFirst()
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res.add(num)
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for (next in graph.getValue(num)) {
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inDegrees[next] = inDegrees[next]!! - 1
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if (inDegrees[next] == 0) {
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queue.add(next)
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}
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}
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}
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return res.toIntArray().contentEquals(nums)
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}
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private fun constructDirectedGraph(
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seq: List<Int>,
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graph: MutableMap<Int, MutableSet<Int>>,
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inDegrees: MutableMap<Int, Int>
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) {
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for (i in 1 until seq.size) {
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val num1 = seq[i - 1]
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val num2 = seq[i]
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if (!graph.getValue(num1).contains(num2)) {
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graph.getValue(num1).add(num2)
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inDegrees[num2] = inDegrees[num2]!! + 1
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}
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}
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}
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}
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fun main() {
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Solution().sequenceReconstruction(
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intArrayOf(1, 2, 3),
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listOf(
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listOf(1, 2),
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listOf(1,3),
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)
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).print()
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Solution().sequenceReconstruction(
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intArrayOf(1, 2, 3),
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listOf(
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listOf(1, 2),
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listOf(1,3),
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listOf(2,3),
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)
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).print()
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}

‎src/com/blankj/structure/MultiDimensionArray.kt

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package com.blankj.structure
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object MultiDimensionArray {
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public fun createTestData(data: String): Array<IntArray> {
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val rows = data.trim().substring(2, data.length - 2) // Remove outer brackets
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val rowStrings = rows.split("],[").toTypedArray() // Split by "],["
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val result = Array(rowStrings.size) {
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rowStrings[it].split(",").map { it.toInt() }.toIntArray() // Convert to integers
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}
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return result
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}
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}

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