【树】【回溯】leetcode_112_路径总和

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    bool hasPathSum(TreeNode* root, int targetSum) {
        if(root == nullptr) return false;
        return traversal(root, targetSum-root->val);
    }

    bool traversal (TreeNode* cur, int count){
        if (cur->left == nullptr && cur ->right == nullptr && count==0) return true;
        if (cur->left == nullptr && cur ->right == nullptr && count!=0) return false;

        if (cur->left != nullptr){
            count = count - cur->left->val;
            bool re = traversal(cur->left, count);
            if (re) return true;
            count += cur->left->val;
        }

        if (cur->right != nullptr){
            count = count - cur->right->val;
            bool re = traversal(cur->right, count);
            if (re) return true;
            count += cur->right->val;
        }
        return false;


    }
};