链接:https://leetcode.com/problems/sum-of-left-leaves/
原题:
Find the sum of all left leaves in a given binary tree.
Example:
3
/ \
9 20
/ \
15 7
There are two left leaves in the binary tree, with values 9 and 15 respectively. Return 24.
分析：这种题就是递归，，
public class Solution {
public int sumOfLeftLeaves(TreeNode root) {
if (root == null) {
return 0;
}
int num =0;
if(root.left!=null && root.left.left == null && root.left.right == null){
num+=root.left.val;
}
return num + sumOfLeftLeaves(root.left) + sumOfLeftLeaves(root.right);
}
}
