572. Subtree of Another Tree

use 100 same tree to complete

time: O(n)

space: O(n)

idea like this, 把 s 所有子樹都檢查 => 是否跟 t 為同一個樹

    public boolean isSubtree(TreeNode s, TreeNode t) {
        if (s == null) return false;
        if (isSameTree(s, t)) return true;
        return isSubtree(s.left, t) || isSubtree(s.right, t);
    }

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