贪心 Codeforces Round #135 (Div. 2) C. Color Stripe

 1 /*
 2     贪心：当m == 2时，结果肯定是ABABAB或BABABA，取最小改变量；当m > 2时，当与前一个相等时， 改变一个字母
 3             同时不和下一个相等就是最优的解法
 4 */
 5 #include <cstdio>
 6 #include <cstring>
 7 #include <algorithm>
 8 using namespace std;
 9 
10 const int MAXN = 5e5 + 10;
11 const int INF = 0x3f3f3f3f;
12 char s[MAXN];
13 
14 int main(void)  {       //Codeforces Round #135 (Div. 2) C. Color Stripe
15     //freopen ("C.in", "r", stdin);
16 
17     int n, m;
18     while (scanf ("%d%d", &n, &m) == 2) {
19         scanf ("%s", s + 1);    int len = strlen (s + 1);
20 
21        if (m == 2)    {
22             int c1 = 0, c2 = 0;
23             for (int i=1; i<=len; ++i)  {
24                 if (i & 1)  {
25                     if (s[i] == ‘A‘)    c2++;
26                     else    c1++;
27                 }
28                 else    {
29                     if (s[i] == ‘A‘)    c1++;
30                     else    c2++;
31                 }
32             }
33 
34             printf ("%d\n", min (c1, c2));
35             for (int i=1; i<=len; ++i)  {
36                 if (i & 1)  printf ("%c", (c1 < c2) ? ‘A‘ : ‘B‘);
37                 else    printf ("%c", (c1 < c2) ? ‘B‘ : ‘A‘);
38             }
39             puts ("");
40         }
41         else    {
42             int ans = 0;    s[len+1] = s[0] = ‘@‘;
43             for (int i=2; i<=len; ++i)  {
44                 if (s[i] == s[i-1]) {
45                     ans++;
46                     for (int j=1; j<=m; ++j)    {
47                         char ch = ‘A‘ + j - 1;
48                         if (s[i] == ch || s[i+1] == ch) continue;
49                         else    {
50                             s[i] = ch;  break;
51                         }
52                     }
53                 }
54             }
55             printf ("%d\n", ans);   s[len+1] = ‘\0‘;
56             printf ("%s\n", s + 1);
57         }
58     }
59 
60     return 0;
61 }