[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);
     }
 }