p112

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LeetCode p112 Path Sum 题解

1.题目：

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.

题意：

输入一个树和一个给定值sum,判断树中是否有条路径和值为sum.

2.解题思路:

见代码

3.代码

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/**
 * 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 (sum == 0 && (root.left == null && root.right == null))
			return true;

		return hasPathSum(root.left, sum) || hasPathSum(root.right, sum);
    }
}

4.一些总结：