leetcode404. Sum of Left Leaves

404. Sum of Left Leaves

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.

解法

递归找出每个结点的左结点再相加。

/**
 * 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) {
        if (root == null) {
            return 0;
        }
        int ans = 0;
        if (root.left != null) {
            if (root.left.left == null && root.left.right == null) {
                ans += root.left.val;
            } else {
                ans += sumOfLeftLeaves(root.left);
            }
        }
        ans += sumOfLeftLeaves(root.right);
        return ans;
    }
}