LeetCode -- Path Sum

LeetCode -- Path Sum

題目描述：


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.




就是從根到葉子，判斷是否存在和為sum的路徑。


思路：


一道典型的DFS題，遍歷時累加當前節點數即可。


實現代碼：

public bool HasPathSum(TreeNode root, int sum) {
        Find(root, 0, sum);
        return found;
    }
    
    private bool found = false;
    
    private void Find(TreeNode node, int sum, int target){
        if(found || node == null){
            return;
        }
        if(node.left == null && node.right == null){
		if(sum + node.val == target){
            		found = true;
        	}
	}
        
        
        Find(node.left, sum + node.val, target);
        Find(node.right, sum + node.val, target);
    }