题意:求包含49的数字，先求不包含的，然后减一下就行了
链接：点我
如果不懂这种数位dp代码，可以看我博客dp专题里的初探数位dp
1 #include<cstdio> 2 #include<iostream> 3 #include<algorithm> 4 #include<cstring> 5 #include<cmath> 6 #include<queue> 7 #include<map> 8 using namespace std; 9 #define MOD 1000000007 10 const int INF=0x3f3f3f3f; 11 const double eps=1e-5; 12 typedef __int64 ll; 13 #define cl(a) memset(a,0,sizeof(a)) 14 #define ts printf("***** "); 15 const int MAXN=105; 16 int n,m,tt; 17 ll dp[MAXN][2]; //0表示前面不为4 18 int digit[MAXN]; 19 ll dfs(int p,int s,bool e) { 20 if (p==-1) return 1; 21 if (!e &&dp[p][s]!=-1) return dp[p][s]; 22 ll res = 0; 23 int u = e?digit[p]:9; 24 for (int i=0;i<=u;++i) 25 { 26 if(s==1&&i==9) continue; 27 res+=dfs(p-1,i==4,e&&i==u); 28 } 29 return e?res:dp[p][s]=res; 30 } 31 ll solve(ll n) 32 { 33 int len=0; 34 while(n) 35 { 36 digit[len++]=n%10; 37 n/=10; 38 } 39 return dfs(len-1,0,1); 40 } 41 int main() 42 { 43 int i,j,k; 44 #ifndef ONLINE_JUDGE 45 freopen("1.in","r",stdin); 46 #endif 47 scanf("%d",&tt); 48 ll x; 49 memset(dp,-1,sizeof(dp)); 50 while(tt--) 51 { 52 scanf("%I64d",&x); 53 printf("%I64d ",x-solve(x)+1); 54 } 55 }