Solution026.java

package com.portgas;

public class Solution026 {

    public static class TreeNode {
        public int val;
        public TreeNode left;
        public TreeNode right;

        public TreeNode(int val) {
            this.val = val;
        }
    }

    /**
     * 树的子结构：
     * 输入两棵二叉树A，B，判断B是不是A的子结构。
     * （ps：我们约定空树不是任意一个树的子结构）
     **/
    public boolean hasSubtree(TreeNode root1, TreeNode root2) {
        if (root1 == null || root2 == null) {
            return false;
        }
        return isSubtree(root1, root2) || isSubtree(root1.left, root2) || isSubtree(root1.right, root2);
    }

    private boolean isSubtree(TreeNode root1, TreeNode root2) {
        if (root2 == null) {
            return true;
        }
        if (root1 == null) {
            return false;
        }

        if (root1.val == root2.val) {
            return isSubtree(root1.right, root2.right) && isSubtree(root1.left, root2.left);
        }

        return false;
    }
}