[Leetcode] 404. Sum of Left Leaves 解题报告
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题目:
Find the sum of all left leaves in a given binary tree.
Example:
3 / \ 9 20 / \ 15 7There are two left leaves in the binary tree, with values 9 and 15 respectively. Return 24.
思路:
一般情况下,树问题最好的解决方法都是递归,本题也不例外。这里的关键点是判断某结点的左孩子是否是叶子结点,如果是,则参与求和,否则递归求解;对于右孩子,则直接递归求解即可。
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 val = 0; TreeNode *left = root->left; if(left && !left->left && !left->right) { // root->left is a leaf val += root->left->val; } val += sumOfLeftLeaves(root->left); val += sumOfLeftLeaves(root->right); return val; }};
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