代码

#include <cstdio>
#include <algorithm>

int d[10];

// lexicographical_order: 11.888 ms
void lexicographical_order(const int size)
{
    int tot = 1, i, j;
    for (i = 0; i < size; i++) d[i] = i+1, tot *= i+1;
    // for (i = 0; i < size; i++) printf("%d%c", d[i], i==size-1?'\n':' ');
    while (--tot)
    {
        i = size - 2;
        while (d[i] > d[i+1]) i--;
        j = size - 1;
        while (j != i) {
            if (d[j] > d[i]) {
                std::swap(d[j], d[i]);
                break;
            } else j--;
        }
        i++;
        j = size - 1;
        while (i < j) {
            std::swap(d[i], d[j]);
            i++; j--;
        }
        // for (i = 0; i < size; i++) printf("%d%c", d[i], i==size-1?'\n':' ');
    }
}

// incremental_way: 87.111 ms
void incremental_way(const int size)
{
    int p[10], tot = 1, i, j, k, l;
    for (i = 0; i < size; i++) d[i] = i+1, tot *= i+1, p[i] = tot;
    tot = 0;
    // for (i = 0; i < size; i++) printf("%d%c", d[i], i==size-1?'\n':' ');
    while (++tot < p[size-1])
    {
        i = 0;
        while (tot % p[i+1] == 0) i++;
        j = 0;
        k = 0;
        for (j = 0; j < size; j++) {
            if (d[j] <= i+1) {
                d[j] = i+2 - d[j];
                k = j;
            } else if (d[j] == i+2) {
                std::swap(d[j], d[k]);
            }
        }
        // for (i = 0; i < size; i++) printf("%d%c", d[i], i==size-1?'\n':' ');
    }
}

// decremental_way: 5.057 ms
void decremental_way(const int size)
{
    int tot = 1, i, j, k, l;
    for (i = 0; i < size; i++) d[i] = i+1, tot *= i+1;
    k = size - 1;
    // for (i = 0; i < size; i++) printf("%d%c", d[i], i==size-1?'\n':' ');
    while (--tot)
    {
        i = 0; while (d[i] + i == size) i++;
        if (i) {
            j = i; while (j < size) {
                if (d[j] == size-i) d[j-i] = d[j-i-1], d[j-i-1] = d[j]; else d[j-i] = d[j];
                j++;
            }
            j = i; while (j) d[size-j] = size-j+1, j--;
            k = size - 1;
        } else {
            l = d[k], d[k] = d[k-1], d[k-1] = l;
            // std::swap(d[k], d[k-1]);
            k--;
        }
        // for (i = 0; i < size; i++) printf("%d%c", d[i], i==size-1?'\n':' ');
    }
}

int main()
{
    // lexicographical_order(10);
    // incremental_way(10);
    decremental_way(10);
    return 0;
}

评测结果