leetcode_112

题目来源：https://leetcode.com/problems/path-sum/

代码：
/**

• 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) {

  int s = 0;
   return dfs(root,sum,s);
  

  }
  public boolean dfs(TreeNode root, int sum,int s){

  if(root == null){
      return false;
  }
  if(root.left == null && root.right == null){
      //到达叶节点，判断和是否等于sum
      s += root.val;
      if(s == sum){
          return true;
      }
  }
  s += root.val;
  //递归
  boolean left = dfs(root.left,sum,s);
  boolean right = dfs(root.right,sum,s);
  if(left||right){
      return true;
  }
  return false;
  

  }
  }