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LeetCode-Easy刷題(26) 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.


判斷是否存在從根節點到葉子節點的值相加結果為給定的值,存在返回true,否則false;


 //深度優先  維護要完成的剩餘目標值
    public boolean hasPathSum(TreeNode root, int sum) {

        if(root ==null){//以最後空接點作為遞迴結束
            return false;
        }
        //滿足題意的結束條件
        if(root.left ==null && root.right ==null && root.val == sum){
            return true;
        }
        return hasPathSum(root.left, sum - root.val) || hasPathSum(root.right, sum - root.val) ;
    }