队列&栈//最小栈

设计一个支持 push，pop，top 操作，并能在常数时间内检索到最小元素的栈。

• push(x) -- 将元素 x 推入栈中。
• pop() -- 删除栈顶的元素。
• top() -- 获取栈顶元素。
• getMin() -- 检索栈中的最小元素。

示例:

MinStack minStack = new MinStack();
minStack.push(-2);
minStack.push(0);
minStack.push(-3);
minStack.getMin();   --> 返回 -3.
minStack.pop();
minStack.top();      --> 返回 0.
minStack.getMin();   --> 返回 -2.

class MinStack {
    private Stack<Integer> s1 = new Stack<>();
    private Stack<Integer> s2 = new Stack<>();
    /** initialize your data structure here. */
    public MinStack() {
        
    }
    
    public void push(int x) {
        s1.push(x);
        if(s2.isEmpty()||s2.peek()>=x)
            s2.push(x);
    }
    
    public void pop() {
        int x = s1.pop();
        if(s2.peek()==x)
            s2.pop();
    }
    
    public int top() {
        return s1.peek();
    }
    
    public int getMin() {
        return s2.peek();
    }
}

/**
 * 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();
 */

class MinStack {
    private int min_val = Integer.MAX_VALUE;
    private Stack<Integer> s = new Stack<>();
    /** initialize your data structure here. */
    public MinStack() {
        
    }
    
    public void push(int x) {
        if(x <= min_val){
            s.push(min_val);
            min_val = x;
        }
        s.push(x);
    }
    
    public void pop() {
        if(s.pop()==min_val)
            min_val = s.pop();
    }
    
    public int top() {
        return s.peek();
    }
    
    public int getMin() {
        return min_val;
    }
}

/**
 * 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();
 */

class MinStack {
private:
    stack<int> s1,s2;    
public:
    /** initialize your data structure here. */
    MinStack() {
    }
    
    void push(int x) {
        s1.push(x);
        if(s2.empty()||x<=s2.top())
            s2.push(x);
    }
    
    void pop() {
        if(s1.top()==s2.top())
            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();
 */

class MinStack {
public:
    /** initialize your data structure here. */
    MinStack() {
        min_val = INT_MAX;
    }
    
    void push(int x) {
        if(x <= min_val)
        {
            st.push(min_val);
            min_val = x;
        }
        st.push(x);
    }
    
    void pop() {
        int t = st.top();
        st.pop();
        if(t == min_val){
            min_val = st.top();
            st.pop();
        }
    }
    
    int top() {
        return st.top();
    }
    
    int getMin() {
        return min_val;
    }
private:
    int min_val;
    stack<int> st;
};

/**
 * 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();
 */