题目介绍

计算给定二叉树的所有左叶子之和。

示例

3
   / 
  9  20
    /  
   15   7

在这个二叉树中，有两个左叶子，分别是 9 和 15，所以返回 24

解法一

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number}
 */
var sumOfLeftLeaves = function(root) {
          
   
  let sum = 0
  if(!root) {
          
   
    return sum;
  }
  let left = root.left, right = root.right;
  if(left) {
          
   
    if(left.left || left.right) {
          
   
      sum += sumOfLeftLeaves(left);
    } else {
          
   
      sum += left.val;
    }
  }
  if(right) {
          
   
    if(right.left || right.right) {
          
   
      sum += sumOfLeftLeaves(right);
    }
  }
  return sum;
};

执行用时 : 84 ms, 在所有 JavaScript 提交中击败了51.41%的用户

内存消耗 : 34 MB, 在所有 JavaScript 提交中击败了58.33%的用户

解法二

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number}
 */
var sumOfLeftLeaves = function(root) {
          
   
  if(root === null) {
          
   
    return 0;
  }
  let temp = [root], sum = 0;
  while (temp.length) {
          
   
    let i = 0, tArray = [];
    while(i < temp.length) {
          
   
      let node = temp[i++];
      let left = node.left;
      let right = node.right;
      if(left) {
          
   
        if(left.left || left.right) {
          
   
          tArray.push(left)
        } else {
          
   
          sum += left.val;
        }
      }
      if(right && (right.left || right.right)) {
          
   
        tArray.push(right)
      }
    }
    temp = tArray;
  }
  return sum;
};

执行用时 : 88 ms, 在所有 JavaScript 提交中击败了51.41%的用户

内存消耗 : 34.7 MB, 在所有 JavaScript 提交中击败了30.56%的用户