179_Largest_Number

qiyuangong · qiyuangong · commit d8eed519d5a3 · 2018-11-30T22:33:51.000+08:00
diff --git a/README.md b/README.md
@@ -74,6 +74,7 @@ Also, there are open source implementations for basic data structs and algorithm
 | 166 | [Fraction to Recurring Decimal](https://leetcode.com/problems/fraction-to-recurring-decimal/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/166_Fraction_to_Recurring_Decimal.py) | % and Hash to find duplicate |
 | 167 | [Two Sum II - Input array is sorted](https://leetcode.com/problems/two-sum-ii-input-array-is-sorted/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/167_Two_Sum_II_Input_array_is_sorted.py) | Two points O(n) and O(1) |
 | 170 | [Two Sum III - Data structure design](https://leetcode.com/problems/two-sum-iii-data-structure-design/) &hearts; | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/170_Two_Sum_III-Data_structure_design.py) | 1. Hash, O(1) for add, O(n) for find, O(n) space<br>2. sorted list, O(logn) for add, O(n) for find, O(n) space<br> 3. Sort before find, O(1) for add, O(nlogn) for find, O(n) space|
+| 179 | [Largest Number](https://leetcode.com/problems/largest-number/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/179_Largest_Number.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/179_Largest_Number.java) | Define a comparator with str(x) + str(y) > str(y) + str(x), O(nlgn) and O(n) |
 | 186 | [Reverse Words in a String II](https://leetcode.com/problems/reverse-words-in-a-string-ii/) &hearts;| [Python](https://github.com/qiyuangong/leetcode/blob/master/python/186_Reverse_Words_in_a_String_II.py) | Reverse all and reverse each words |
 | 198 | [House Robber](https://leetcode.com/problems/house-robber/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/198_House_Robber.py) | f(k) = max(f(k – 2) + num[k], f(k – 1)), O(n) and O(1) |
 | 200 | [Number of Islands](https://leetcode.com/problems/number-of-islands/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/200_Number_of_Islands.py) | 1. Quick union find, O(nlogn) and O(n^2)<br>2. BFS with marks, O(n^2) and O(1) |
diff --git a/java/179_Largest_Number.java b/java/179_Largest_Number.java
@@ -0,0 +1,35 @@
+class Solution {
+    private class LargerNumberComparator implements Comparator<String> {
+        @Override
+        public int compare(String a, String b) {
+            String order1 = a + b;
+            String order2 = b + a;
+           return order2.compareTo(order1);
+        }
+    }
+
+    public String largestNumber(int[] nums) {
+        // Get input integers as strings.
+        String[] asStrs = new String[nums.length];
+        for (int i = 0; i < nums.length; i++) {
+            asStrs[i] = String.valueOf(nums[i]);
+        }
+
+        // Sort strings according to custom comparator.
+        Arrays.sort(asStrs, new LargerNumberComparator());
+
+        // If, after being sorted, the largest number is `0`, the entire number
+        // is zero.
+        if (asStrs[0].equals("0")) {
+            return "0";
+        }
+
+        // Build largest number from sorted array.
+        String largestNumberStr = new String();
+        for (String numAsStr : asStrs) {
+            largestNumberStr += numAsStr;
+        }
+
+        return largestNumberStr;
+    }
+}
diff --git a/python/179_Largest_Number.py b/python/179_Largest_Number.py
@@ -0,0 +1,9 @@
+class LargerNumKey(str):
+    def __lt__(x, y):
+        return x + y > y + x
+
+
+class Solution:
+    def largestNumber(self, nums):
+        largest_num = ''.join(sorted(map(str, nums), key=LargerNumKey))
+        return '0' if largest_num[0] == '0' else largest_num
