LeetCode: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.

AC:

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