【LeetCode】分类刷题之栈和队列

STL

栈：std::stack<int> S;
S.top() S.empty() S.push(x) S.pop() S.size()
队列：std:queue<int> Q;
Q.empty()、Q.front()、Q.back()、Q.pop()、Q.push()、Q.size()

题225 用队列实现栈

用时：0ms 100% 内存 7MB 100%

class MyStack {
public:/** Initialize your data structure here. */MyStack() {}/** Push element x onto stack. */void push(int x) {std::queue<int> temp_queue;temp_queue.push(x);while(!data_queue.empty()){int a = _data.front();temp_queue.push(a);_data.pop();}while(!temp_queue.empty()){data_queue.push(temp_queue.front());temp_queue.pop();}}/** Removes the element on top of the stack and returns that element. */int pop() {int x = data_queue.front();data_queue.pop();return x;}/** Get the top element. */int top() {return data_queue.front();}/** Returns whether the stack is empty. */bool empty() {return data_queue.empty();}
private:std::queue<int> data_queue;
};/*** 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();*/

题232 用栈实现队列

用时：0ms 100% 内存 7.2MB 100%

class MyQueue {
public:/** Initialize your data structure here. */MyQueue() {}/** Push element x to the back of queue. */void push(int x) {std::stack<int> temp_stack;while(!data_stack.empty()){temp_stack.push(data_stack.top());data_stack.pop();}temp_stack.push(x);while(!temp_stack.empty()){data_stack.push(temp_stack.top());temp_stack.pop();}}/** Removes the element from in front of queue and returns that element. */int pop() {int x = data_stack.top();data_stack.pop();return x;}/** Get the front element. */int peek() {return data_stack.top();}/** Returns whether the queue is empty. */bool empty() {return data_stack.empty();}
private:std::stack<int> data_stack;
};/*** Your MyQueue object will be instantiated and called as such:* MyQueue* obj = new MyQueue();* obj->push(x);* int param_2 = obj->pop();* int param_3 = obj->peek();* bool param_4 = obj->empty();*/

题155 最小栈

用时：40ms 43.19% 内存：15.2MB 100%

class MinStack {
public:/** initialize your data structure here. */std::stack<int> data;std::stack<int> min_data;MinStack() {}void push(int x) {data.push(x);if(min_data.empty()){min_data.push(x);}else{if(x < min_data.top()){min_data.push(x);}else{min_data.push(min_data.top());}}}void pop() {data.pop();min_data.pop();//最小值栈中最小值的位置和原来栈中位置是一致的//所以可以同时弹出}int top() {return data.top();}int getMin() {return min_data.top();}
};/*** Your MinStack object will be instantiated and called as such:* MinStack* obj = new MinStack();* obj->push(x);* obj->pop();* int param_3 = obj->top();* int param_4 = obj->getMin();*/

题946 验证栈序列

给定 pushed 和 popped 两个序列，每个序列中的值都不重复，只有当它们可能是在最初空栈上进行的推入 push 和弹出 pop 操作序列的结果时，返回 true；否则，返回 false 。
示例 1：
输入：pushed = [1,2,3,4,5], popped = [4,5,3,2,1]
输出：true
解释：我们可以按以下顺序执行：
push(1), push(2), push(3), push(4), pop() -> 4,
push(5), pop() -> 5, pop() -> 3, pop() -> 2, pop() -> 1
示例 2：
输入：pushed = [1,2,3,4,5], popped = [4,3,5,1,2]
输出：false
解释：1 不能在 2 之前弹出。
提示：
0 <= pushed.length == popped.length <= 1000
0 <= pushed[i], popped[i] < 1000
pushed 是 popped 的排列。

用 $j$ 指针指向数组 $p o p p e d$ 可以模拟队列，数组 $p u s h e d$ 存在栈中。如果栈顶元素和队列元素，则同时弹出。如果栈空，则合法。否则，不合法。

class Solution {
public:bool validateStackSequences(vector<int>& pushed, vector<int>& popped) {std::stack<int> s;int n = pushed.size();int j = 0;//poped索引//将pushed压栈for(int i = 0; i < n; i++){s.push(pushed[i]);while(!s.empty()&&s.top()==popped[j]){s.pop();j++;}}return s.empty();}  
};