[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.

题解：采用减法。

code：

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