1046 Last Stone Weight Solution

Author: dipti95

typescript/1046-Last-Stone-Weight.ts

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+class MaxHeap {
+  heap: number[]
+  constructor(array: number[]) {
+    this.heap = this.buildHeap(array)
+  }
+
+  buildHeap(array: number[]) {
+    let parentIdx = Math.floor((array.length - 2) / 2)
+    for (let i = parentIdx; i >= 0; i--) {
+      this.siftDown(i, array.length - 1, array)
+    }
+    return array
+  }
+
+  siftDown(idx: number, endIdx: number, heap: number[]) {
+    let childOneIdx = 2 * idx + 1
+
+    while (childOneIdx <= endIdx) {
+      let childTwoIdx = 2 * idx + 2 <= endIdx ? 2 * idx + 2 : -1
+      let swapIdx
+      if (childTwoIdx !== -1 && heap[childOneIdx] < heap[childTwoIdx]) {
+        swapIdx = childTwoIdx
+      } else swapIdx = childOneIdx
+      if (heap[swapIdx] > heap[idx]) {
+        this.swap(swapIdx, idx, heap)
+        idx = swapIdx
+        childOneIdx = 2 * idx + 1
+      } else return
+    }
+  }
+
+  siftUp(idx: number, heap: number[]) {
+    let parentIdx = Math.floor((idx - 1) / 2)
+    while (heap[parentIdx] < heap[idx] && idx > 0) {
+      this.swap(parentIdx, idx, heap)
+      idx = parentIdx
+      parentIdx = Math.floor((idx - 1) / 2)
+    }
+  }
+
+  peek() {
+    return this.heap[0]
+  }
+
+  remove() {
+    this.swap(this.heap.length - 1, 0, this.heap)
+    const removeValue = this.heap.pop()
+    this.siftDown(0, this.heap.length - 1, this.heap)
+    return removeValue
+  }
+
+  size() {
+    return this.heap.length
+  }
+
+  insert(value: number) {
+    this.heap.push(value)
+    this.siftUp(this.heap.length - 1, this.heap)
+  }
+  swap(i: number, j: number, arr: number[]) {
+    let ele = arr[i]
+    arr[i] = arr[j]
+    arr[j] = ele
+  }
+}
+
+function lastStoneWeight(stones: number[]): number {
+  const heap = new MaxHeap(stones)
+
+  while (heap.size() > 1) {
+    const stone1 = heap.remove()
+    const stone2 = heap.remove()
+
+    heap.insert(stone1 - stone2)
+  }
+
+  return heap.peek()
+}