LeetCode-Same Tree & Symmetric Tree-蒲公英云

LeetCode-Same Tree & Symmetric Tree

女爷i 2022-08-06 15:07 252阅读 0赞

两道题放一块了，

一个是判断两棵树是否相同：

Given two binary trees, write a function to check if they are equal or not.

Two binary trees are considered equal if they are structurally identical and the nodes have the same value.

一个是判断一棵树是否对称：

iven a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).

For example, this binary tree is symmetric:

But the following is not:

通过这两道题，可以深刻的体会到树本身递归的特性，用递归求解是非常方便的，代码还非常的简洁：

    public boolean isSameTree(TreeNode p, TreeNode q) {
        if (p == null && q == null) return true;
        else if (p == null || q == null) return false;
        if (p.val != q.val) return false;
        return isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
    }
    public boolean isSymmetric(TreeNode root) {
        if (root == null) return true;
        return dfs(root.left, root.right);
    }
    private boolean dfs(TreeNode left, TreeNode right) {
        if (left == null && right == null) return true;
        else if (left == null || right == null) return false;
        if (left.val != right.val) return false;
        return dfs(left.left, right.right) && dfs(left.right, right.left);
    }