155. Min Stack

155. Min Stack

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.

push(x) – Push element x onto stack.
pop() – Removes the element on top of the stack.
top() – Get the top element.
getMin() – Retrieve the minimum element in the stack.

Example:

MinStack minStack = new MinStack();
minStack.push(-2);
minStack.push(0);
minStack.push(-3);
minStack.getMin(); --> Returns -3.
minStack.pop();
minStack.top(); --> Returns 0.
minStack.getMin(); --> Returns -2.

Analysis:
没怎么遇到过这样的题，没有思路。参考了这两个网址：Min Stack – LeetCode 和 Min Stack

Source Code（C++）:

#include <iostream>
#include <stack>
using namespace std;


class MinStack {
public:
    /** initialize your data structure here. */
    stack<int> stk, minstk;
    MinStack() {

    }

    void push(int x) {
        stk.push(x);
        if (minstk.empty() || x<=minstk.top())  //注意此处必须有=
        {
            minstk.push(x);
        }
    }

    void pop() {
        int top=stk.top();
        stk.pop();
        if (top==minstk.top()){
            minstk.pop();
        }
    }

    int top() {
        return stk.top();
    }

    int getMin() {
        return minstk.top();
    }
};

int main() {
    MinStack sol;
    return 0;
}