Q112. Path Sum
直达:https://leetcode.com/problems/path-sum/description/
Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.
For example:
Given the below binary tree and
sum = 22
5
/ \
4 8
/ / \
11 13 4
/ \ \
7 2 1
return true, as there exist a root-to-leaf path5->4->11->2
which sum is 22.
分析
保存全局变量path计算根节点到该节点的路径长度,递归的计算即可。另外,用全局变量保存叶节点的路径长度是否是sum。
C++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:
bool hasPathSum(TreeNode* root, int sum) {
if(!root) return false;
bool res = false;
treePath(root, root->val, sum, res);
return res;
}
private:
void treePath(TreeNode* root, int path, int sum, bool& res){
if(!root->left && !root->right){
res = res || (path == sum);
return;
}
if(root->left) treePath(root->left, path+root->left->val, sum, res);
if(root->right) treePath(root->right, path+root->right->val, sum, res);
}
};
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