Min Stack

LeetCode #155

Description:

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.

Idea:

Code:

class MinStack {
public:
    /** initialize your data structure here. */
    MinStack() {

    }

    void push(int x) {
        stack_data.push(x);
        if(stack_min.empty()||x<=stack_min.top()) // if x==min 也要入栈
            stack_min.push(x);

    }

    void pop() {
        int element=stack_data.top();
        stack_data.pop();

        if(element==stack_min.top()) stack_min.pop();

    }

    int top() {
        return stack_data.top();
    }

    int getMin() {
        return stack_min.top();

    }

private:
    stack<int> stack_data;
    stack<int> stack_min;
};

/**
 * 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();
 */