题解 | #[NOIP2015]金币#

#include <stdio.h>

int main() {
    int k = 0;

    while (1 == scanf("%d", &k))
    {
        // 初始的金币数为1个
        int gold = 1;
        // 总的金币数
        int sum_gold = 0;
        int sum_day = 0;
        
        for (int day = 1; sum_day <= k; )
        {
            if ((k - sum_day) >= day)
            {
                sum_gold += (day * gold++);
                sum_day += (day++);
            }
            else 
            {
                sum_gold += (gold * (k - sum_day));
                break;
            }
        }
        printf("%d\n", sum_gold);
    }
    
    return 0;
}