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[Java教程][LeetCode] Path Sum


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.

 

     这道题挺简单的,直接用recursive做就可以了。因为反正每一个node检查的方式都一样。

     只要目前的sum减去正在检查的node的value之后等于0,就可以return true。

     所以程序还是很简单的。

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