572. Subtree of Another Tree

题目地址:https://leetcode.com/problems/subtree-of-another-tree/description/

Given two non-empty binary trees s and t, check whether tree t has exactly the same structure and node values with a subtree of s. A subtree of s is a tree consists of a node in s and all of this node's descendants. The tree s could also be considered as a subtree of itself.

Example 1:
Given tree s:

     3
    / 
   4   5
  / 
 1   2

Given tree t:

   4 
  / 
 1   2

Return true, because t has the same structure and node values with a subtree of s.

Example 2:
Given tree s:

     3
    / 
   4   5
  / 
 1   2
    /
   0

Given tree t:

   4
  / 
 1   2

Return false.

因为CSDN的java模版有问题，无法显示null，这里改用c++模版显示

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public boolean isSubtree(TreeNode s, TreeNode t) {
        if (s == null || t == null) return s == t;
        if (isSame(s, t))   return true;
        return isSubtree(s.left, t) || isSubtree(s.right, t);
    }
    public boolean isSame(TreeNode s, TreeNode t) {
        if (s == null || t == null) return s == t;
        return s.val == t.val && isSame(s.left, t.left) && isSame(s.right, t.right);
    }
}

题目输入的测试是s是[3, 4, 5, 1, 2, null, null, 0]，t是[4, 1, 2]的形式，从上到下按层遍历建树

Debug code in playground:

/* -----------------------------------
 *  WARNING:
 * -----------------------------------
 *  Your code may fail to compile
 *  because it contains public class
 *  declarations.
 *  To fix this, please remove the
 *  "public" keyword from your class
 *  declarations.
 */

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public boolean isSubtree(TreeNode s, TreeNode t) {
        if (s == null || t == null) return s == t;
        if (isSame(s, t))   return true;
        return isSubtree(s.left, t) || isSubtree(s.right, t);
    }
    public boolean isSame(TreeNode s, TreeNode t) {
        if (s == null || t == null) return s == t;
        return s.val == t.val && isSame(s.left, t.left) && isSame(s.right, t.right);
    }
}

public class MainClass {
    public static TreeNode stringToTreeNode(String input) {
        input = input.trim();
        input = input.substring(1, input.length() - 1);
        if (input.length() == 0) {
            return null;
        }
    
        String[] parts = input.split(",");
        String item = parts[0];
        TreeNode root = new TreeNode(Integer.parseInt(item));
        Queue<TreeNode> nodeQueue = new LinkedList<>();
        nodeQueue.add(root);
    
        int index = 1;
        while(!nodeQueue.isEmpty()) {
            TreeNode node = nodeQueue.remove();
    
            if (index == parts.length) {
                break;
            }
    
            item = parts[index++];
            item = item.trim();
            if (!item.equals("null")) {
                int leftNumber = Integer.parseInt(item);
                node.left = new TreeNode(leftNumber);
                nodeQueue.add(node.left);
            }
    
            if (index == parts.length) {
                break;
            }
    
            item = parts[index++];
            item = item.trim();
            if (!item.equals("null")) {
                int rightNumber = Integer.parseInt(item);
                node.right = new TreeNode(rightNumber);
                nodeQueue.add(node.right);
            }
        }
        return root;
    }
    
    public static String booleanToString(boolean input) {
        return input ? "True" : "False";
    }
    
    public static void main(String[] args) throws IOException {
        BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
        String line;
        while ((line = in.readLine()) != null) {
            TreeNode s = stringToTreeNode(line);
            line = in.readLine();
            TreeNode t = stringToTreeNode(line);
            
            boolean ret = new Solution().isSubtree(s, t);
            
            String out = booleanToString(ret);
            
            System.out.print(out);
        }
    }
}

========================================Talk is cheap, show me the code=======================================