155.min-stack.cpp

#include <bits/stdc++.h>
using namespace std;

// @lc code=start
class MinStack
{
private:
    stack<int> mainStack;
    stack<int> minStack;

public:
    MinStack() {}

    void push(int val)
    {
        mainStack.push(val);
        if (minStack.empty() || minStack.top() >= val)
        {
            minStack.push(val);
        }
    }

    void pop()
    {
        if (mainStack.top() == minStack.top())
        {
            minStack.pop();
        }
        mainStack.pop();
    }

    int top()
    {
        return mainStack.top();
    }
    int getMin()
    {
        return minStack.top();
    }
};
// @lc code=end

/*
 * @lc app=leetcode id=155 lang=cpp
 *
 * [155] Min Stack
 *
 * https://leetcode.com/problems/min-stack/description/
 *
 * algorithms
 * Medium (56.60%)
 * Likes:    15324
 * Dislikes: 959
 * Total Accepted:    2.3M
 * Total Submissions: 4.1M
 * Testcase Example:  '["MinStack","push","push","push","getMin","pop","top","getMin"]\n' +
  '[[],[-2],[0],[-3],[],[],[],[]]'
 *
 * Design a stack that supports push, pop, top, and retrieving the minimum
 * element in constant time.
 *
 * Implement the MinStack class:
 *
 *
 * MinStack() initializes the stack object.
 * void push(int val) pushes the element val onto the stack.
 * void pop() removes the element on the top of the stack.
 * int top() gets the top element of the stack.
 * int getMin() retrieves the minimum element in the stack.
 *
 *
 * You must implement a solution with O(1) time complexity for each
 * function.
 *
 *
 * Example 1:
 *
 *
 * Input
 * ["MinStack","push","push","push","getMin","pop","top","getMin"]
 * [[],[-2],[0],[-3],[],[],[],[]]
 *
 * Output
 * [null,null,null,null,-3,null,0,-2]
 *
 * Explanation
 * MinStack minStack = new MinStack();
 * minStack.push(-2);
 * minStack.push(0);
 * minStack.push(-3);
 * minStack.getMin(); // return -3
 * minStack.pop();
 * minStack.top();    // return 0
 * minStack.getMin(); // return -2
 *
 *
 *
 * Constraints:
 *
 *
 * -2^31 <= val <= 2^31 - 1
 * Methods pop, top and getMin operations will always be called on non-empty
 * stacks.
 * At most 3 * 10^4 calls will be made to push, pop, top, and getMin.
 *
 *
 */