572. Subtree of Another Tree

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.

//用先序遍历的方法，本解法思路：s的值和t的值不同则跳出，相同，则继续比左子树，直到都指向空。才判定两者值相等

class Solution {

    public boolean isSubtree(TreeNode s, TreeNode t) {

        if (s == null) return false;

        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 true;

        if (s == null || t == null) return false;

        if (s.val != t.val) return false;

        return isSame(s.left, t.left) && isSame(s.right, t.right);

    }

}