LeetCode OJ 112. 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.

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解答

其实只要注意叶节点时的处理就可以了。

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */
 int flag = false;
void DFS(struct TreeNode *root, int sum){
    if(root == NULL){
        return;
    }
    ){
        flag = true;
    }
    DFS(root->left, sum - root->val);
    DFS(root->right, sum - root->val);
}
bool hasPathSum(struct TreeNode* root, int sum) {
    flag = false;
    DFS(root, sum);
    return flag;
}