[Leetcode]112. Path Sum -David_Lin

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


思路：递归所有路径，如果到达叶子节点，并且此时sum=0，则返回true;

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public boolean hasPathSum(TreeNode root, int sum) {
        if (root==null)
            return flase;            //一开始如果传进来空引用，则返回false;
        sum-=root.val;
        if (root.left==null&&&root.right==null){    //如果已经到了叶子
            if (sum==0)                                        //如果此时sum=0，则返回true
                return true;                                     //否则返回false
            else 
                return false;
        }
        //同时递归左右子树
        return hasPathSum(root.left,sum)||hasPathSum(root.right,sum);
    }
}