剑指 Offer 30. 包含min函数的栈

思路#

方法一：辅助栈 (单调栈)#

这里参考：面试题30. 包含 min 函数的栈（辅助栈，清晰图解）

相似题目：剑指 Offer 59 - I. 滑动窗口的最大值

 

 

class MinStack {
private:
    stack<int> A;
    stack<int> B;
public:
    /** initialize your data structure here. */
    MinStack() {
        
    }
    
    void push(int x) {
        A.push(x);
        //这里不能写x < B.top()，否则下面这种输入过不了
        /*
            ["MinStack","push","push","push","getMin","pop","getMin"]
            [[],[0],[1],[0],[],[],[]]
        */
        if(B.empty() || x <= B.top()) {
            B.push(x);
        }
    }
    
    void pop() {
        if(A.top() == B.top())
            B.pop();
        A.pop();
    }
    
    int top() {
        return A.top();
    }
    
    int getMin() {
        return B.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();
 */

 

方法二：一个栈同时保存当前值和栈内最小值#

这里参考：一个栈同时保存当前值和栈内最小值

class MinStack {
private:
    stack<pair<int, int>> S;
public:
    /** initialize your data structure here. */
    MinStack() {

    }
    
    void push(int x) {
        if(S.empty())
            S.push(make_pair(x, x));
        else
            S.push( make_pair(x, std::min(x, S.top().second)) );
    }
    
    void pop() {
        S.pop();
    }
    
    int top() {
        return S.top().first;
    }
    
    int min() {
        return S.top().second;
    }
};

/**
 * 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->min();
 */