901.online-stock-span.cpp

/*
 * @lc app=leetcode id=901 lang=cpp
 *
 * [901] Online Stock Span
 *
 * https://leetcode.com/problems/online-stock-span/description/
 *
 * algorithms
 * Medium (50.64%)
 * Total Accepted:    12.4K
 * Total Submissions: 24.5K
 * Testcase Example:  '["StockSpanner","next","next","next","next","next","next","next"]\n[[],[100],[80],[60],[70],[60],[75],[85]]'
 *
 * 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.
 * 
 * 
 * 
 */
class StockSpanner {
public:
    vector<int> prices;
    vector<int> dp;
    StockSpanner() {
        prices.clear();
        dp.clear();
    }
    
    int next(int price) {
        int ret = 1;
        int i = prices.size()-1;
        while(i>=0 && prices[i] <= price){
            ret += dp[i];
            i = i - dp[i];
        }
        prices.push_back(price);
        dp.push_back(ret);
        return ret;
    }
};

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