155. Min Stack

无名_1989

于 2018-03-05 08:34:58 发布

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本文介绍了一个特殊的数据结构——最小值栈，它能在常数时间内完成压栈、弹栈、获取栈顶元素及获取当前栈中最小元素的操作。通过两个栈的巧妙配合，确保了操作效率。

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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.

Example:

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

class MinStack {
private:
    stack<int> s1;
    stack<int> s2;
public:
    void push(int x) {
	    s1.push(x);
	    if (s2.empty() || x <= getMin())  s2.push(x);	    
    }
    void pop() {
	    if (s1.top() == getMin())  s2.pop();
	    s1.pop();
    }
    int top() {
	    return s1.top();
    }
    int getMin() {
	    return s2.top();
    }
};