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

题目传送门

 /*
     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
             同时不和下一个相等就是最优的解法
 */
 #include <cstdio>
 #include <cstring>
 #include <algorithm>
 using namespace std;

 const int MAXN = 5e5 + ;
 const int INF = 0x3f3f3f3f;
 char s[MAXN];

 int main(void)  {       //Codeforces Round #135 (Div. 2) C. Color Stripe
     //freopen ("C.in", "r", stdin);

     int n, m;
     while (scanf ("%d%d", &n, &m) == ) {
         scanf ("%s", s + );    int len = strlen (s + );

        if (m == )    {
             int c1 = , c2 = ;
             for (int i=; i<=len; ++i)  {
                 if (i & )  {
                     if (s[i] == 'A')    c2++;
                     else    c1++;
                 }
                 else    {
                     if (s[i] == 'A')    c1++;
                     else    c2++;
                 }
             }

             printf ("%d\n", min (c1, c2));
             for (int i=; i<=len; ++i)  {
                 if (i & )  printf ("%c", (c1 < c2) ? 'A' : 'B');
                 else    printf ("%c", (c1 < c2) ? 'B' : 'A');
             }
             puts ("");
         }
         else    {
             int ans = ;    s[len+] = s[] = '@';
             for (int i=; i<=len; ++i)  {
                 if (s[i] == s[i-]) {
                     ans++;
                     for (int j=; j<=m; ++j)    {
                         char ch = 'A' + j - ;
                         if (s[i] == ch || s[i+] == ch) continue;
                         else    {
                             s[i] = ch;  break;
                         }
                     }
                 }
             }
             printf ("%d\n", ans);   s[len+] = '\0';
             printf ("%s\n", s + );
         }
     }

     return ;
 }