LeetCode[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.

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思路：须要两个栈，一个用来作为一般的栈，还有一个用来存放进栈到某一位置的当前站内最小元素。代码例如以下：

Code（c++）:

class MinStack {
public:
    std::stack<int> stk;
    std::stack<int> min;
    void push(int x) {
        stk.push(x);
        if(min.empty() || (!min.empty() && x <= min.top())){
            min.push(x);
        }
    }

    void pop() {
        if(!stk.empty()){
            if(stk.top() == min.top())min.pop();
            stk.pop();
        }
    }

    int top() {
        if(!stk.empty())
            return stk.top();
    }

    int getMin() {
        if(!stk.empty()) return min.top();
    }
};

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