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.

题解：

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