leetcode112----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.

解题思路：

递归拆分子问题：

1.root为空 返回fasle

2.root是叶子节点 且root.val==sum 返回true

3.递归拆分 左节点或者右节点满足 都返回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 false;
		if(root.left==null&&root.right==null&&root.val==sum)
			return true;
		else
			return hasPathSum(root.left, sum-root.val)||hasPathSum(root.right, sum-root.val);
    }
}