LeetCode 112. Path Sum

Posted 2020-08-04

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.

这个题目其实就是二叉树的遍历，我采用深度遍历

 

/**
 * 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:
    void depthFirstSearch(TreeNode* root, int sum, bool &tag)
    {
        if (root==NULL)return;
        if (root->left)
        {
            depthFirstSearch(root->left, sum - root->val, tag);
            depthFirstSearch(root->right, sum - root->val, tag);
        }
        else
        {
            if (root->right)
            {
                if (root->right->right == NULL&&root->right->left == NULL)
                {
                    if (sum - root->val - root->right->val == 0)tag = true;
                    return;
                }
                else
                {
                    depthFirstSearch(root->right->left, sum - root->val - root->right->val, tag);
                    depthFirstSearch(root->right->right, sum - root->val - root->right->val, tag);
                }
            }
            else
            {
                if (0 == sum-root->val)tag = true;
            }
        }
    }
    bool hasPathSum(TreeNode* root, int sum) {
        bool tag = false;
        depthFirstSearch(root, sum, tag);
        return tag;
    }
};