[leetcode 155] Min Stack

原创于 2015-01-05 22:14:38 发布 · 220 阅读

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本文介绍了一个支持 push、pop、top 操作及常数时间获取最小元素的栈实现，通过两个栈结构 s1 和 s2 来完成这一任务。

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.

class MinStack {
public:
    void push(int x) {
        s1.push(x);
        if (s2.empty() || s2.top() >= x) {
            s2.push(x);
        }
    }

    void pop() {
        int t = s1.top();
        s1.pop();
        if (s2.top() == t) {
            s2.pop();
        }
    }

    int top() {
        return s1.top();
    }

    int getMin() {
        return s2.top();
    }
private:
    stack<int> s1;
    stack<int> s2;
};