pat 乙级 1030 完美数列

关键是qsort函数和滑动窗口

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
int max(int a, int b)
{
    return a > b ? a : b;
}
int cmp(const void *a, const void *b)
{
    return *(int *)a - *(int *)b;
}
int main()
{
    int n, p;
    scanf("%d %d", &n, &p);
    int num[n];
    for (int i = 0; i < n; i++)
    {
        scanf("%d", &num[i]);
    }
    qsort(num, n, sizeof(num[0]), cmp);
    int left = 0;
    int right = 0;
    int maxlen = 0;
    while (right < n && left < n)
    {
        if ((long long)num[left] * p >= (long long)num[right])
        {
            ++right;
            maxlen = max(maxlen, right - left);
        }
        else
        {
            ++left;
        }
    }
    printf("%d", maxlen);
    return 0;
}