[LeetCode] 404.Sum of Left Leaves

• 题目描述
• 解题思路
• 实验代码

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题目描述

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.

解题思路

这道题的要点是怎样找到要加的数对应的节点，搞清楚树的结构以及特点就能知道，左叶节点需要满足的条件是：1.非空；2.无子节点。想到这两个条件以后利用树中常用的递归就能解决这个问题。

实验代码

/** * 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 sum = 0;    void preorder(TreeNode* root) {        if (root == NULL)            return;        TreeNode* T = root->left;        if (T != NULL && T->left == NULL && T->right == NULL)            sum += T->val;        preorder(root->left);        preorder(root->right);    }    int sumOfLeftLeaves(TreeNode* root) {        preorder(root);        return sum;    }};