HDU 5787：K-wolf Number（数位DP）

题目链接：http://acm.split.hdu.edu.cn/showproblem.php?pid=5787

题意：要求相邻的K个位的数不能相同，在[L,R]区间有多少个这样的数.

 #include <cstdio>
 #include <cstring>
 #include <algorithm>
 using namespace std;

 int bit[];
 long long dp[][][][][];
 int k;

 //考虑前导零:d = 10代表前一位是0, 当(d == 10 && u == 0)表示当前这位为0并且前4位都是0

 bool check(int a, int b, int c, int d, int u)
 {
     if(k == ) return u != d;
     else if(k == ) return u != d && u != c;
     else if(k == ) return u != d && u != c && u != b;
     else return u != d && u != c && u != b && u != a;
 }

 long long dfs(int pos, int a, int b, int c, int d, bool flag)
 {
     if(pos <= ) return d != ;
     long long res = dp[pos][a][b][c][d];
     if(flag && res != -) return res;
     long long ans = ;
     int up = flag ?  : bit[pos];
     for(int u = ; u <= up; u++) {
         if(d ==  && u == ) {
             ans += dfs(pos - , a, b, c, d, flag || u != up);
         } else if(check(a, b, c, d, u)) {
             ans += dfs(pos - , b, c, d, u, flag || u != up);
         }
     }
     if(flag) dp[pos][a][b][c][d] = ans;
     return ans;
 }

 long long solve(long long x)
 {
     int len = ;
     while(x) {
         bit[++len] = x % ;
         x /= ;
     }
     return dfs(len, , , , , );
 }

 int main()
 {
     long long l, r;
     while(~scanf("%I64d%I64d%d", &l, &r, &k)) {
         memset(dp, -, sizeof(dp));
         printf("%I64d\n", solve(r) - solve(l - ));
     }
     return ;
 }

另一种：

 #include <cstdio>
 #include <cstring>
 #include <algorithm>
 using namespace std;

 int bit[];
 long long dp[][][][][][];
 int k;

 //考虑前导零:d = 10代表前一位是0, 当(d == 10 && u == 0)表示当前这位为0并且前4位都是0

 bool check(int a, int b, int c, int d, int u)
 {
     if(k == ) return u != d;
     else if(k == ) return u != d && u != c;
     else if(k == ) return u != d && u != c && u != b;
     else return u != d && u != c && u != b && u != a;
 }

 long long dfs(int pos, int a, int b, int c, int d, bool flag, bool zero)
 {
     if(pos <= ) return zero;
     long long res = dp[pos][a][b][c][d][zero];
     if(flag && res != - && zero) return res;
     long long ans = ;
     int up = flag ?  : bit[pos];
     for(int u = ; u <= up; u++) {
         if(!zero && u == ) {
             ans += dfs(pos - , a, b, c, d, flag || u != up, );
         } else if(check(a, b, c, d, u)) {
             ans += dfs(pos - , b, c, d, u, flag || u != up, );
         }
     }
     if(flag) dp[pos][a][b][c][d][zero] = ans;
     return ans;
 }

 long long solve(long long x)
 {
     int len = ;
     while(x) {
         bit[++len] = x % ;
         x /= ;
     }
     return dfs(len, , , , , , );
 }

 int main()
 {
     long long l, r;
     while(~scanf("%I64d%I64d%d", &l, &r, &k)) {
         memset(dp, -, sizeof(dp));
         printf("%I64d\n", solve(r) - solve(l - ));
     }
     return ;
 }