[LeetCode] Path Sum

Question:

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.

1、题型分类:

2、思路:采用递归,需要注意的是left和right不能分开递归返回,否则可能出现left不存在但是right不存在,但是left先返回的情况

3、时间复杂度:

4、代码:

    public boolean hasPathSum(TreeNode root, int sum) {
        if(root!=null) sum=sum-root.val;else return false;
        if(root.left==null && root.right==null && sum==0) return true;
        if(root.left!=null || root.right!=null) 
            return hasPathSum(root.left, sum)  || hasPathSum(root.right, sum);
        return false;
    }

 

5、优化:

6、扩展:

posted @ 2015-07-14 11:45  Maydow  阅读(125)  评论(0编辑  收藏  举报