USACOTrainning.Prime Palindromes
题目大意是给两个整数a,b，然后求出这之间的所有回文素数。
枚举回文的数，其实枚举回文的数加上判断宿舍的时间不是很长的。
1
#include
<
iostream
>
2
#include
<
string
>
3
#include
<
algorithm
>
4
#include
<
string
.h
>
5
#include
<
vector
>
6
#include
<
math.h
>
7
#include
<
time.h
>
8
#include
<
queue
>
9
#include
<
set
>
10
using
namespace
std;
11
12
vector
<
int
>
ans;
13
14
int
num[
8
];
15
16
bool
check(
int
val)
17
{
18
for
(
int
i
=
2
; i
<=
sqrt(val
*
1.0
); i
++
)
19
{
20
if
(val
%
i
==
0
)
return
false
;
21
}
22
return
true
;
23
}
24
25
void
dfs(
int
i,
int
len)
26
{
27
if
(i
==
len)
28
{
29
int
val
=
0
;
30
for
(
int
j
=
0
; j
<
2
*
len; j
++
)
31
{
32
if
(j
<
len) val
=
val
*
10
+
num[j];
33
else
val
=
val
*
10
+
num[
2
*
len
-
1
-
j];
34
}
35
if
(check(val)) ans.push_back(val);
36
return
;
37
}
38
39
if
(i
==
0
)
40
{
41
for
(
int
j
=
1
; j
<=
9
; j
+=
2
)
42
{
43
//
if(j == 5) continue;
44
num[i]
=
j;
45
dfs(i
+
1
, len);
46
}
47
}
48
else
49
{
50
for
(
int
j
=
0
; j
<=
9
; j
++
)
51
{
52
num[i]
=
j;
53
dfs(i
+
1
, len);
54
}
55
}
56
}
57
58
void
ddfs(
int
i,
int
len)
59
{
60
if
(i
==
len)
61
{
62
int
val
=
0
;
63
for
(
int
j
=
0
; j
<
2
*
len
-
1
; j
++
)
64
{
65
if
(j
<
len) val
=
val
*
10
+
num[j];
66
else
val
=
val
*
10
+
num[
2
*
len
-
2
-
j];
67
}
68
if
(check(val)) ans.push_back(val);
69
return
;
70
}
71
72
if
(i
==
0
)
73
{
74
for
(
int
j
=
1
; j
<=
9
; j
+=
2
)
75
{
76
//
if(j == 5) continue;
77
num[i]
=
j;
78
ddfs(i
+
1
, len);
79
}
80
}
81
else
82
{
83
for
(
int
j
=
0
; j
<=
9
; j
++
)
84
{
85
num[i]
=
j;
86
ddfs(i
+
1
, len);
87
}
88
}
89
}
90
91
void
ready()
92
{
93
for
(
int
i
=
1
; i
<=
8
; i
++
)
94
{
95
if
(i
%
2
==
0
) dfs(
0
, i
/
2
);
96
else
ddfs(
0
, i
/
2
+
1
);
97
}
98
}
99
100
int
main()
101
{
102
freopen(
"
pprime.in
"
,
"
r
"
, stdin);
103
freopen(
"
pprime.out
"
,
"
w
"
, stdout);
104
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ready();
106
sort(ans.begin(), ans.end());
107
int
a, b, res
=
0
;
108
scanf(
"
%d%d
"
,
&
a,
&
b);
109
for
(
int
i
=
0
; i
<
ans.size(); i
++
)
110
{
111
if
(ans[i]
>=
a
&&
ans[i]
<=
b) printf(
"
%d\n
"
, ans[i]);
112
}
113
}