LeetCode: Path Sum

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 path 5->4->11->2 which sum is 22.

解题分析：

找路径问题，找到满足和为指定的数的路径，若找到这样的路径，则返回true，否则返回false.

可以使用深度优先搜索的思想进行递归求解，若当前结点为NULL，返回false，若当前结点为叶子结点，且符合条件，则返回true，否则递归判断其左右子树。

代码如下：

bool hasPathSum(TreeNode *root, int sum) {        if (root == NULL) return false;        if (root->val == sum && root->left ==  NULL && root->right == NULL) return true;        return hasPathSum(root->left, sum-root->val) || hasPathSum(root->right, sum-root->val);    }