Min Stack

题目：

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.

分析： 求最小值的方式有一定参考价值，每次栈顶记录此栈的最小值

代码：

class MinStack {public:    /** initialize your data structure here. */        stack<int>stac;    stack<int>minstack;    MinStack() {            }        void push(int x) {        if(stac.empty())        {            stac.push(x);            minstack.push(x);        }        else        {            stac.push(x);            minstack.push(min(x,minstack.top()));        }    }        void pop() {        stac.pop();        minstack.pop();    }        int top() {        return stac.top();    }        int getMin() {        return minstack.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(); */