[leetcode] 404. Sum of Left Leaves

Description

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

题目的意思是：求二叉树左叶子节点的和。

• 树模型一般用递归的方法，终止条件当然是该节点为空。如果左子节点存在，且左叶子节点没有子节点，那么该左节点为题目要求的节点。然后继续递归找出所有的左叶子节点。

代码

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int sumOfLeftLeaves(TreeNode* root) {
        if(!root){
            return 0;
        }
        int sum=0;
        if(root->left&&!root->left->left&& !root->left->right){
            return root->left->val+sumOfLeftLeaves(root->right);
        }

        return sumOfLeftLeaves(root->left)+sumOfLeftLeaves(root->right);
    }
};

参考文献

​​[LeetCode] Sum of Left Leaves 左子叶之和​​