1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
|
_static int64_t factorial(int64_t);
_static bool isperm(uint8_t *, int64_t);
_static int64_t permtoindex(uint8_t *, int64_t);
_static void indextoperm(int64_t, int64_t, uint8_t *);
_static int permsign(uint8_t *, int64_t);
_static int64_t
factorial(int64_t n)
{
int64_t i, ret;
if (n > _max_factorial) {
LOG("Error: won't compute factorial for n=%" PRId64 " because"
" it is larger than %" PRId64 "\n", n, _max_factorial);
return -1;
}
if (n < 0)
return 0;
for (i = 1, ret = 1; i <= n; i++)
ret *= i;
return ret;
}
_static bool
isperm(uint8_t *a, int64_t n)
{
int64_t i;
bool aux[_max_factorial+1];
if (n > _max_factorial) {
LOG("Error: won't compute 'isperm()' for n=%" PRId64 " because"
" it is larger than %" PRId64 "\n", n, _max_factorial);
return false;
}
memset(aux, false, n);
for (i = 0; i < n; i++) {
if (a[i] < 0 || a[i] >= n)
return false;
else
aux[a[i]] = true;
}
for (i = 0; i < n; i++)
if (!aux[i])
return false;
return true;
}
_static int64_t
permtoindex(uint8_t *a, int64_t n)
{
int64_t i, j, c, ret;
if (n > _max_factorial) {
LOG("Error: won't compute 'permtoindex()' for n=%" PRId64
" because it is larger than %" PRId64 "\n",
n, _max_factorial);
return -1;
}
if (!isperm(a, n))
return -1;
for (i = 0, ret = 0; i < n; i++) {
for (j = i+1, c = 0; j < n; j++)
c += (a[i] > a[j]) ? 1 : 0;
ret += factorial(n-i-1) * c;
}
return ret;
}
_static void
indextoperm(int64_t p, int64_t n, uint8_t *r)
{
int64_t i, j, c;
uint8_t a[_max_factorial+1];
if (n > _max_factorial) {
LOG("Error: won't compute 'permtoindex()' for n=%" PRId64
" because it is larger than %" PRId64 "\n",
n, _max_factorial);
goto indextoperm_error;
}
memset(a, 0, n);
if (p < 0 || p >= factorial(n))
goto indextoperm_error;
for (i = 0; i < n; i++) {
for (j = 0, c = 0; c <= p / factorial(n-i-1); j++)
c += a[j] ? 0 : 1;
r[i] = j-1;
a[j-1] = 1;
p %= factorial(n-i-1);
}
if (!isperm(r, n))
goto indextoperm_error;
return;
indextoperm_error:
memset(r, _error, n);
}
_static int
permsign(uint8_t *a, int64_t n)
{
int i, j;
uint8_t ret;
for (i = 0, ret = 0; i < n; i++)
for (j = i+1; j < n; j++)
ret += a[i] > a[j] ? 1 : 0;
return ret % 2;
}
|
