155. Min Stack （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.

class MinStack {
public:
    /** initialize your data structure here. */
    MinStack() {
       minValues.push(INT_MAX);
    }
    
    void push(int x) {
        if(x<=minValues.top()){
            minValues.push(x);
        }
        
        allValues.push(x);
    }
    
    void pop() {
        if(allValues.top()==minValues.top()){
            minValues.pop();
        }
        
        allValues.pop();
    }
    
    int top() {
        return allValues.top();
    }
    
    int getMin() {
        return minValues.top();
    }
private:
    stack<int> allValues;
    stack<int> minValues;
};

/**
 * 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();
 */