#LeetCode 155 (#剑指offer 30)

Problem Description

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.

class MinStack {
public:
    //Create two empty stacks.
    stack<int> c;   
    stack<int> m;   //Min stack;

    void push(int val) {
        //When min stack is empty or val less and equal the top element 
        //Equal condition can avoid val be push more time.
        //At first,i don't write equal condition,it waste me more time
        if (m.empty() || val <= getMin())   
            m.push(val);    //push val into min stack
        c.push(val);
    }
    
    void pop() {
        if (c.top() == getMin())    
            m.pop();    //Update the min stack top element.
        c.pop();
    }
    
    int top() {
        return c.top();
    }
    
    int getMin() {
        return m.top();
    }
};

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