【HDOJ】3183 A Magic Lamp

RMQ。

 /* 3183 */
 #include <cstdio>
 #include <cstring>
 #include <cstdlib>

 #define MAXN 1005

 char s[MAXN], ans[MAXN];
 int dp[MAXN][MAXN];
 int n,len,m;

 int min(int x, int y) {
     return s[x]<=s[y] ? x:y;
 }

 void RMQ_init() {
     int i, j, k;

     for (i=; i<=len; ++i)
         dp[i][] = i;
     for (j=; (<<j)<=len; ++j)
         for (i=; i+(<<j)-<=len; ++i)
             dp[i][j] = min(dp[i][j-], dp[i+(<<(j-))][j-]);
 }

 int RMQ(int l, int r) {
     int k = ;

     while ((<<(k+)) <= r-l+)
         ++k;
     return min(dp[l][k], dp[r-(<<k)+][k]);
 }

 int main() {
     int i, j, k;
     int l;

     #ifndef ONLINE_JUDGE
         freopen("data.in", "r", stdin);
         freopen("data.out", "w", stdout);
     #endif

     while (scanf("%s %d", s+, &m)!=EOF) {
         len = strlen(s+);
         RMQ_init();
         m = len - m;
         l = k = ;
         while (m--) {
             k = RMQ(k, len-m);
             ans[l++] = s[k++];
         }
         for (i=; i<l; ++i)
             if (ans[i] != '')
                 break;
         ans[l] = '\0';
         if (i == l)
             puts("");
         else
             puts(ans+i);
     }

     return ;
 }