Online Stock Span_your bank object will be instantiated and called a-优快云博客

本文链接：https://blog.youkuaiyun.com/u013325815/article/details/106639821

本文介绍了一个名为StockSpanner的类，该类收集股票每日价格并返回当前价格的跨度。跨度定义为从今天开始向后连续的天数，这些天的股票价格小于或等于今天的价格。通过使用单调递减栈，我们可以有效地计算出每天的股票跨度。

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Write a class StockSpanner which collects daily price quotes for some stock, and returns the span of that stock's price for the current day.

The span of the stock's price today is defined as the maximum number of consecutive days (starting from today and going backwards) for which the price of the stock was less than or equal to today's price.

For example, if the price of a stock over the next 7 days were [100, 80, 60, 70, 60, 75, 85], then the stock spans would be [1, 1, 1, 2, 1, 4, 6].

Example 1:

Input: ["StockSpanner","next","next","next","next","next","next","next"], [[],[100],[80],[60],[70],[60],[75],[85]]
Output: [null,1,1,1,2,1,4,6]
Explanation: 
First, S = StockSpanner() is initialized.  Then:
S.next(100) is called and returns 1,
S.next(80) is called and returns 1,
S.next(60) is called and returns 1,
S.next(70) is called and returns 2,
S.next(60) is called and returns 1,
S.next(75) is called and returns 4,
S.next(85) is called and returns 6.

Note that (for example) S.next(75) returned 4, because the last 4 prices
(including today's price of 75) were less than or equal to today's price.

Note:

Calls to StockSpanner.next(int price) will have 1 <= price <= 10^5.
There will be at most 10000 calls to StockSpanner.next per test case.
There will be at most 150000 calls to StockSpanner.next across all test cases.
The total time limit for this problem has been reduced by 75% for C++, and 50% for all other languages.

思路：单调递减栈，也就是进来一个数，跟前面的数比较，如果peek <= value，pop，用node记录days和value，为什么要用days而不用count记录pop多少次，原因是，pop的次数，后面是不知道的，那么只能通过days来记录前面有多少个被pop出去了，所以只有记录days才行。记录历史的value和days即可；T: O(N); S: O(N)

class StockSpanner {
    private class Node {
        public int days;
        public int value;
        public Node(int days, int value) {
            this.days = days;
            this.value = value;
        }
    }

    private Stack<Node> stack;
    private int days;
    public StockSpanner() {
        this.stack = new Stack<Node>();
        this.days = 0;
    }
    
    public int next(int price) {
        int res = 0;
        Node node = new Node(++days, price);
        while(!stack.isEmpty() && stack.peek().value <= price) {
            stack.pop();
        }
        if(stack.isEmpty()) {
            res = node.days;
        } else {
            res = days - stack.peek().days;
        }
        stack.push(node);
        return res;
    }
}

/**
 * Your StockSpanner object will be instantiated and called as such:
 * StockSpanner obj = new StockSpanner();
 * int param_1 = obj.next(price);
 */