题目链接：http://acm.timus.ru/problem.aspx?space=1&num=1057
题意：求[L,R]区间内的数转换成b进制后可以变成k个b进制的幂和。
其实就是求区间内的数里有几个数，使得这些数转换成b进制有k个1存在。
转换成对应进制，然后dfs。每一位插0或者1就行了。（这题其实前导零不用处理）
1 #include <bits/stdc++.h> 2 using namespace std; 3 #define fr first 4 #define sc second 5 #define cl clear 6 #define BUG puts("here!!!") 7 #define W(a) while(a--) 8 #define pb(a) push_back(a) 9 #define Rint(a) scanf("%d", &a) 10 #define Rll(a) scanf("%I64d", &a) 11 #define Rs(a) scanf("%s", a) 12 #define Cin(a) cin >> a 13 #define FRead() freopen("in", "r", stdin) 14 #define FWrite() freopen("out", "w", stdout) 15 #define Rep(i, len) for(int i = 0; i < (len); i++) 16 #define For(i, a, len) for(int i = (a); i < (len); i++) 17 #define Cls(a) memset((a), 0, sizeof(a)) 18 #define Clr(a, x) memset((a), (x), sizeof(a)) 19 #define Full(a) memset((a), 0x7f7f7f, sizeof(a)) 20 #define lrt rt << 1 21 #define rrt rt << 1 | 1 22 #define pi 3.14159265359 23 #define RT return 24 #define lowbit(x) x & (-x) 25 #define onecnt(x) __builtin_popcount(x) 26 typedef long long LL; 27 typedef long double LD; 28 typedef unsigned long long ULL; 29 typedef pair<int, int> pii; 30 typedef pair<string, int> psi; 31 typedef pair<LL, LL> pll; 32 typedef map<string, int> msi; 33 typedef vector<int> vi; 34 typedef vector<LL> vl; 35 typedef vector<vl> vvl; 36 typedef vector<bool> vb; 37 38 const int maxn = 33; 39 int dp[maxn][maxn][2]; 40 int digit[maxn]; 41 int x, y, k, b; 42 43 int mul(int x, int n) { 44 int ret = 1; 45 while(n) { 46 if(n & 1) ret *= x; 47 n >>= 1; x *= x; 48 } 49 return ret; 50 } 51 52 int dfs(int l, int cnt, bool fz, bool flag) { 53 if(l == 0) return cnt == k; 54 if(!flag && ~dp[l][cnt][fz]) return dp[l][cnt][fz]; 55 int ret = 0; 56 int pos = flag ? digit[l] : b-1; 57 Rep(i, min(pos+1, 2)) { 58 if(i==0 && fz) ret += dfs(l-1, cnt, true, flag&&(i==pos)); 59 else ret += dfs(l-1, cnt+i, fz&&(i==0), flag&&(i==pos)); 60 } 61 if(!flag) dp[l][cnt][fz] = ret; 62 return ret; 63 } 64 65 int f(int t) { 66 int pos = 0; 67 while(t) { 68 digit[++pos] = t % b; 69 t /= b; 70 } 71 return dfs(pos, 0, true, true); 72 } 73 74 signed main() { 75 //FRead(); 76 Clr(dp, -1); 77 while(~scanf("%d%d%d%d",&x,&y,&k,&b)) { 78 printf("%d ", f(y) - f(x-1)); 79 } 80 RT 0; 81 }