Create 1046-Last-Stone-Weight.js

bbawj · web-flow · commit afc1fc68d155 · 2022-07-13T21:50:08.000+08:00
diff --git a/javascript/1046-Last-Stone-Weight.js b/javascript/1046-Last-Stone-Weight.js
@@ -0,0 +1,72 @@
+class Heap {
+    constructor(stones){
+        this.heap = stones
+        this.size = stones.length
+        this.heapify(0)
+    }
+    right(pos) {
+        return 2*pos + 2
+    }
+    left(pos) {
+        return 2*pos + 1
+    }
+    isleaf(pos) {
+        if (2*pos + 1 >= this.size) return true
+        return false
+    }
+    swap(a,b){
+        let temp = this.heap[a]
+        this.heap[a] = this.heap[b]
+        this.heap[b] = temp
+    }
+    fix(pos){
+        if (this.isleaf(pos)) return
+        let left = this.left(pos)
+        let right = this.right(pos)
+        let bigger = left
+        if (right < this.size) bigger = this.heap[left] > this.heap[right] ? left : right
+        if (this.heap[pos] < this.heap[bigger]) {
+            this.swap(pos,bigger)
+            this.fix(bigger)
+        }
+    }
+    heapify(pos){
+        if (this.isleaf(pos)) return
+        this.heapify(this.left(pos))
+        this.heapify(this.right(pos))
+        this.fix(pos)
+    }
+    delete(){
+        this.swap(0, --this.size)
+        this.fix(0)
+        return this.heap[0]
+    }
+    insert(val){
+        this.size++
+        this.heap[this.size-1] = val
+        this.heapify(0)
+    }
+    peek(){
+        return this.heap[0]
+    }
+}
+/**
+ * @param {number[]} stones
+ * @return {number}
+ */
+var lastStoneWeight = function(stones) {
+    //use a max heap to pop off the top 2 stones at each time
+    //if result is 0 we can do nothing
+    //if the result is a new weight we can push it back to the heap
+    const heap = new Heap(stones)
+    while(heap.size > 1) {
+        let x = heap.peek()
+        heap.delete()
+        let y = heap.peek()
+        heap.delete()
+        const res = x-y
+        if (res > 0) heap.insert(res)
+    }
+    if (heap.size) return heap.peek()
+    return 0
+};
