Leetcode剑指Offer刷题 - 第七天

 Leetcode剑指Offer刷题指南：

Leetcode剑指Offer刷题-学习计划目录_DEGv587的博客-CSDN博客

 剑指 Offer 26. 树的子结构

解法：递归

class Solution {
    public boolean isSubStructure(TreeNode A, TreeNode B) {
        if (A == null || B == null) {
            return false;
        }
        return dfs(A, B) || isSubStructure(A.left, B) || isSubStructure(A.right, B);
    }

    private boolean dfs(TreeNode A, TreeNode B) {
        if (B == null) return true;
        if (A == null) return false;

        return A.val == B.val && dfs(A.left, B.left) && dfs(A.right, B.right);
    }
}

剑指 Offer 27. 二叉树的镜像

解法：递归

class Solution {
    public TreeNode mirrorTree(TreeNode root) {
        if (root == null) return null;

        TreeNode tmp = root.left;
        root.left = mirrorTree(root.right);
        root.right = mirrorTree(tmp);

        return root;
    }
}

剑指 Offer 28. 对称的二叉树

class Solution {
    public boolean isSymmetric(TreeNode root) {
        if (root == null) return true;

        return dfs(root.left, root.right);
    }

    private boolean dfs(TreeNode root1, TreeNode root2) {
        if (root1 == null && root2 == null) return true;
        if (root1 == null || root2 == null) return false;

        return root1.val == root2.val && dfs(root1.left, root2.right) && dfs(root1.right, root2.left);
    }
}