blob: 6200c4c6b0a682a7736e34e2b555bdf6679722f4 (
plain)
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
|
#include <string>
using std::string;
class Solution
{
public:
void longestWithCenter(const string &s, int length, int index, int *longest_start, int *longest_length_ptr)
{
int &longest_length = *longest_length_ptr;
int palindrome_length_odd = index * 2 + 1 <= longest_length || (length - index - 1) * 2 + 1 <= longest_length ? 0 : 1;
int palindrome_length_even = (index + 1) * 2 <= longest_length || (length - index - 1) * 2 <= longest_length ? 0 : 1;
while (palindrome_length_odd || palindrome_length_even)
{
if (palindrome_length_odd)
{
int start = index - palindrome_length_odd;
int end = index + palindrome_length_odd;
if (start < 0)
{
palindrome_length_odd = 0;
}
else if (end >= length)
{
palindrome_length_odd = 0;
}
else
{
if (s[start] == s[end])
{
int current_length = end - start + 1;
if (current_length > longest_length)
{
*longest_start = start;
longest_length = current_length;
}
palindrome_length_odd++;
}
else
{
palindrome_length_odd = 0;
}
}
}
if (palindrome_length_even)
{
int start = index - palindrome_length_even + 1;
int end = index + palindrome_length_even;
if (start < 0)
{
palindrome_length_even = 0;
}
else if (end >= length)
{
palindrome_length_even = 0;
}
else
{
if (s[start] == s[end])
{
int current_length = end - start + 1;
if (current_length > longest_length)
{
*longest_start = start;
longest_length = current_length;
}
palindrome_length_even++;
}
else
{
palindrome_length_even = 0;
}
}
}
}
}
string longestPalindrome(string s)
{
if (s.empty())
return "";
int longest_start = 0;
int longest_length = 1;
int length = s.size();
for (int i = 0; i < length; i++)
{
longestWithCenter(s, length, i, &longest_start, &longest_length);
}
return s.substr(longest_start, longest_length);
}
};
int main()
{
Solution s{};
s.longestPalindrome("bb");
return 0;
}
|
