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.


设计一个栈，有一个取最小元素的操作

C++（29ms）：   用两个栈

class MinStack {
private:
    stack<int> s1 ;
    stack<int> s2 ;
public:
    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();
 */

C++(29ms):  一个栈  注意用long

class MinStack {
private:
    stack<long> s ;
    
    long Min ;
public:
    void push(int x) {
        if (s.empty()){
            s.push(0) ;
            Min = x ;
        }else{
            s.push(x-Min) ;
            if (x < Min)
                Min = x ;
        }
    }
    
    void pop() {
        if (s.empty())
            return ;
        long top = s.top() ;
        if (top < 0)
            Min -= top ;
        s.pop() ;
    }
    
    int top() {
        long top = s.top() ;
        if (top > 0){
            return (int)top+Min ;
        }else{
            return (int)Min ;
        }
    }
    
    int getMin() {
        return (int)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();
 */