LeetCode (Min Stack)

Problem:

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.

Solution:

class MinStack {private:    stack<int> s1;    stack<int> s2;public:    /** initialize your data structure here. */    MinStack() {            }        void push(int x) {        s1.push(x);        if(s2.empty() || x <= getMin())            s2.push(x);    }        void pop() {        if(s1.top() == getMin())             s2.pop();        s1.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(); */