计算全排列

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#include<bits/stdc++.h>
using namespace std;
bool next_permutation(int a[], int s, int e)
{
    if (s == e)
        return false;
    int i = e;
    int j = i;
    i--;
    while (true)
    {
        if (j == s)
            return false;
        if (a[i] >= a[j])
        {
            j = i;
            i--;
        }
        else
        {
            int k = e;
            while (a[k] < a[i])k--;
            swap(a[i], a[k]);
            reverse(a+i+1, a+e+1);
            return true;
        }
    }
}
int main()
{
    int a[] = {1, 2, 3, 4};
    do {
        for (int i = 0;i < 4;i++)
            cout << a[i] << " ";
        printf("\n");
    }while(next_permutation(a, 0, 3));
    return 0;
}