Leetcode[Easy] - Path Sum

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public boolean hasPathSum(TreeNode root, int sum) {
        TreeNode current = root; 
        return sum(current, 0 ,sum);
    }
    
    public boolean sum(TreeNode current, int s, int gap){
         if(current == null)
             return false;
         if(current.left == null && current.right == null)
             return s+current.val == gap;
         return sum(current.left, s+current.val, gap) || sum(current.right, s+current.val, gap);
    }
}

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HINT:

递归的思想，跌进坑里，够爬一会再出来~~~~

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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.