[LeetCode] 112、路径总和

题目描述

给定一个二叉树和一个目标和，判断该树中是否存在根节点到叶子节点的路径，这条路径上所有节点值相加等于目标和。

示例:
给定如下二叉树，以及目标和 sum = 22，

              5
             / \
            4   8
           /   / \
          11  13  4
         /  \      \
        7    2      1

参考代码

常规题，很经典

/**
 * 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 target) {
        hasPath = false;
        int sum  = 0;
        hasPathSumRecursively(root, sum, target);
        
        return hasPath;
    }
    
    void hasPathSumRecursively(TreeNode* root, int &sum, int target){
        if(root == nullptr)
            return;
            
        sum += root->val;
        if(root->left == nullptr && root->right == nullptr){
            if(sum == target)
                hasPath = true;
        }
        hasPathSumRecursively(root->left, sum, target);
        hasPathSumRecursively(root->right, sum, target);
        sum -= root->val;
    }

private:
    bool hasPath;
};