[LeetCode 225,226][简单]用队列实现栈/翻转二叉树

225.用队列实现栈
题目链接

class MyStack {
public:
    /** Initialize your data structure here. */
    deque<int>mq;
    int tp;
    MyStack() {
        
    }
    
    /** Push element x onto stack. */
    void push(int x) {
        mq.emplace_back(x);
        tp = x;
    }
    
    /** Removes the element on top of the stack and returns that element. */
    int pop() {
        int q = mq.size()-1;
        while(q--){
            tp = mq.front();
            mq.emplace_back(mq.front());
            mq.pop_front();
        }
        int ret = mq.front();
        mq.pop_front();
        return ret;
    }
    
    /** Get the top element. */
    int top() {
        return tp;
    }
    
    /** Returns whether the stack is empty. */
    bool empty() {
        return mq.empty();
    }
};

/**
 * Your MyStack object will be instantiated and called as such:
 * MyStack* obj = new MyStack();
 * obj->push(x);
 * int param_2 = obj->pop();
 * int param_3 = obj->top();
 * bool param_4 = obj->empty();
 */

226.翻转二叉树
题目链接

class Solution {
public:
    TreeNode* invertTree(TreeNode* root) {
        if(root == NULL) return NULL;
        invertTree(root->left);
        invertTree(root->right);
        swap(root->left,root->right);
        return root;
    }
};