Path Sum

题目原型：

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.

              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.

基本思路：

题目基本意思就是说给定一个数sum，自顶向下求一条路径，使得这条路径的和为这个给定值。采用递归，没一层递归时，将sum-1，只要有一条路径符合即可。

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

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Path Sum

原文：http://blog.csdn.net/cow__sky/article/details/20565335