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Commit 6e39eef

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update 4 leetcode
1 parent aaec803 commit 6e39eef

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4 files changed

+224
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4 files changed

+224
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/*
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* @lc app=leetcode id=637 lang=javascript
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*
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* [637] Average of Levels in Binary Tree
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*/
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// @lc code=start
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/**
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* Definition for a binary tree node.
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* function TreeNode(val, left, right) {
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* this.val = (val===undefined ? 0 : val)
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* this.left = (left===undefined ? null : left)
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* this.right = (right===undefined ? null : right)
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* }
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*/
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/**
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* @param {TreeNode} root
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* @return {number[]}
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*/
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/**
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* Definition for a binary tree node.
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* function TreeNode(val, left, right) {
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* this.val = (val===undefined ? 0 : val)
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* this.left = (left===undefined ? null : left)
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* this.right = (right===undefined ? null : right)
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* }
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*/
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/**
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* @param {TreeNode} root
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* @return {number[]}
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*/
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var averageOfLevels = function(root) {
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let queues = [root];
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let level = 0;
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let res = [];
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while (queues.length) {
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let oLen = len = queues.length;
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let sum = 0;
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while (len--) {
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const cur = queues.shift() || {};
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if (cur.val !== null) {
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sum += cur.val;
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}
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cur.left && queues.push(cur.left);
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cur.right && queues.push(cur.right);
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}
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res[level] = sum / oLen;
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level++;
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}
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return res;
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};
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// @lc code=end
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/*
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* @lc app=leetcode id=783 lang=javascript
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*
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* [783] Minimum Distance Between BST Nodes
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*/
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// @lc code=start
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/**
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* Definition for a binary tree node.
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* function TreeNode(val, left, right) {
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* this.val = (val===undefined ? 0 : val)
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* this.left = (left===undefined ? null : left)
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* this.right = (right===undefined ? null : right)
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* }
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*/
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/**
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* 中序遍历的方式
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* 二叉搜索树的特性是任意两节点的差值肯定会比相邻节点的大
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* 下面就只遍历了一次
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* @param {*} root
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* @returns
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*/
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var minDiffInBST = function(root) {
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let ans = Number.MAX_SAFE_INTEGER, pre = -1;
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const dfs = (root) => {
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if (root === null) {
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return;
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}
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dfs(root.left);
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if (pre == -1) {
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pre = root.val;
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} else {
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ans = Math.min(ans, root.val - pre);
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pre = root.val;
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}
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dfs(root.right);
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}
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dfs(root);
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return ans;
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};
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/**
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* 遍历保存所有值,进行排序
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* 再遍历保存差值
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* 复杂度较高
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* @param {TreeNode} root
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* @return {number}
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*/
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var minDiffInBST2 = function(root) {
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let queues = [root];
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let res = [];
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let min = Number.MAX_SAFE_INTEGER;
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while (queues.length) {
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const cur = queues.shift() || {};
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if (cur.val !== null) {
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res.push(cur.val);
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}
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cur.left && queues.push(cur.left);
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cur.right && queues.push(cur.right);
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}
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res = res.sort((a, b) => a - b);
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res.forEach((n, index) => {
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if (index == 0) {
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return;
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}
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if (Math.abs(n - res[index - 1]) < min) {
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min = Math.abs(n - res[index - 1]);
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}
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});
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return min;
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};
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// @lc code=end
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/*
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* @lc app=leetcode id=876 lang=javascript
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*
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* [876] Middle of the Linked List
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*/
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// @lc code=start
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/**
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* Definition for singly-linked list.
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* function ListNode(val, next) {
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* this.val = (val===undefined ? 0 : val)
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* this.next = (next===undefined ? null : next)
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* }
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*/
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/**
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* 快慢指针法
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* @param {ListNode} head
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* @return {ListNode}
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*/
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var middleNode = function(head) {
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let fast = slow = head;
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// 慢的走一步,快的走两步,这样快的走到的时候,慢的正好走到一半
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while (fast && fast.next) {
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slow = slow.next;
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fast = fast.next.next;
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}
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return slow;
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};
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/**
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* 单指针法
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* @param {*} head
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* @returns
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*/
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var middleNode2 = function(head) {
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if (!head.next) {
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return head;
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}
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let h1 = h2 = head;
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let l1 = l2 = 0;
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while (h1.next) {
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h1 = h1.next;
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l1++;
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}
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const mid = ~~((l1 + 1) / 2);
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// 这里也不一定使用循环,可以用数组保存数据,然后直接通过下标访问
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while (l2 < mid) {
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h2 = h2.next;
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l2++;
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}
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return h2;
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};
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// @lc code=end

‎leetcode/938.range-sum-of-bst.js

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/*
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* @lc app=leetcode id=938 lang=javascript
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*
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* [938] Range Sum of BST
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*/
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// @lc code=start
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/**
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* Definition for a binary tree node.
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* function TreeNode(val, left, right) {
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* this.val = (val===undefined ? 0 : val)
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* this.left = (left===undefined ? null : left)
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* this.right = (right===undefined ? null : right)
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* }
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*/
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/**
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* 广度优先的遍历
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* @param {TreeNode} root
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* @param {number} low
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* @param {number} high
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* @return {number}
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*/
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var rangeSumBST = function(root, low, high) {
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let queues = [root];
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let sum = 0;
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while (queues.length) {
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const cur = queues.shift() || {};
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if (cur.val <= high && cur.val >= low) {
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sum += cur.val;
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}
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cur.left && queues.push(cur.left);
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cur.right && queues.push(cur.right);
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}
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return sum;
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};
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// @lc code=end

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