题目描述

设计一个支持push，pop，top等操作并且可以在O(1)时间内检索出最小元素的堆栈。

push(x)–将元素x插入栈中
pop()–移除栈顶元素
top()–得到栈顶元素
getMin()–得到栈中最小元素

样例

MinStack minStack = new MinStack();
minStack.push(-1);
minStack.push(3);
minStack.push(-4);
minStack.getMin();   --> Returns -4.
minStack.pop();
minStack.top();      --> Returns 3.
minStack.getMin();   --> Returns -1.

C++ 代码

class MinStack {
public:
    /** initialize your data structure here. */
    stack<int> s1,s2; //s1存储正常入栈元素 s2存储栈最小元素
    MinStack() {

    }

    void push(int x) {
        s1.push(x);
        if(s2.empty()){
            s2.push(x);
        }
        else{
            s2.push(x>s2.top()?s2.top():x);
        }
    }

    void pop() {
        s1.pop();
        s2.pop();
    }

    int top() {
      return s1.top();
    }

    int getMin() {
       return s2.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();
 */