题目

Find the sum of all left leaves in a given binary tree.

Example:

  1.     3
  2.    / \
  3.   9  20
  4.     /  \
  5.    15   7
  7. There are two left leaves in the binary tree, with values 9 and 15 respectively. Return 24.

题意

求树中所有左叶结点的值之和。

思路

递归遍历判断是不是左叶结点即可。

代码实现

Java

  1. class Solution {
  2.     public int sumOfLeftLeaves(TreeNode root) {
  3.         return dfs(root, false);
  4.     }
  6.     private int dfs(TreeNode p, boolean left) {
  7.         if (p == null) {
  8.             return 0;
  9.         }
  11.         if (p.left == null && p.right == null) {
  12.             return left ? p.val : 0;
  13.         }
  15.         return dfs(p.left, true) + dfs(p.right, false);
  16.     }
  17. }