POJ 3617 - Best Cow Line（字典序最小） 题解

  1 #include<cstdio>
  2 #include<algorithm>
  3 #include<cstring>
  4 
  5 char def[50005],line[50005];
  6 int head,tail,n,tot = 0;
  7 inline void op(int x)
  8 {
  9     if(x == 0)
 10     {
 11         while(head <= tail)
 12             line[++ tot] = def[head ++],line[++ tot] = def[tail --];
 13         return;
 14     }
 15     else if(x == 1)
 16     {
 17         if(def[head] == def[tail])
 18             line[++ tot] = def[head ++];
 19         else if(def[head] < def[tail])
 20         {
 21             line[++ tot] = def[head ++];
 22             return;
 23         }
 24         else if(def[tail] < def[head])
 25         {
 26             line[++ tot] = def[tail --];
 27             return;
 28         }
 29     }
 30     else if(x == 2)
 31     {
 32         if(def[head] == def[tail])
 33             line[++ tot] = def[tail --];
 34         else if(def[head] < def[tail])
 35         {
 36             line[++ tot] = def[head ++];
 37             return;
 38         }
 39         else if(def[tail] < def[head])
 40         {
 41             line[++ tot] = def[tail --];
 42             return;
 43         }
 44     }
 45         
 46 }
 47 
 48 void solve(int l,int r)
 49 {
 50     for(int i = 1;;++ i)
 51     {
 52         if(l >= r)
 53         {
 54             op(0);
 55             break;
 56         }
 57         if(def[l] == def[r])
 58         {
 59             l++,r--;
 60             continue;
 61         }
 62         if(def[l] < def[r])
 63         {
 64             op(1);
 65             break;
 66         }
 67         if(def[r] < def[l])
 68         {
 69             op(2);
 70             break;
 71         }
 72     }
 73 }
 74 
 75 int main()
 76 {
 77     char x;
 78     scanf("%d",&n);
 79     x = getchar();
 80     for(int i = 1;i <= n;++ i)
 81     {
 82         while(x < ‘A‘) x = getchar();
 83         def[i] = x,x = getchar();
 84     }
 85     head = 1,tail = n;
 86     while(head <= tail && tot <= n)
 87     {
 88         if(def[head] < def[tail])
 89             line[++ tot] = def[head ++];
 90         else if(def[tail] < def[head])
 91             line[++ tot] = def[tail --];
 92         else
 93             solve(head,tail);
 94     }
 95     for(int i = 1;i <= n;++ i)
 96     {
 97         putchar(line[i]);
 98         if(i%80 == 0)
 99             putchar(‘\n‘);
100     }
101     return 0;
102 }