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.
一刷
题解：
把tree的问题分解成left和right的subtree问题。用DFS求解
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public int sumOfLeftLeaves(TreeNode root) {
return sum(root, false);
}
private int sum(TreeNode root, boolean isLeft){
if(root == null) return 0;
if(root.left==null && root.right==null && isLeft) {
return root.val;
}
int left = sum(root.left, true);
int right = sum(root.right, false);
return left + right;
}
}
