[Swust OJ 137]--波浪数(hash+波浪数构造)

 1 #include<iostream>
 2 using namespace std;
 3 int x, y, a, b, k;
 4 short Hash[10000001];//占两个字节，减少内存
 5 int Len(int x, int k){
 6     int cnt = 0;
 7     while (x){
 8         x /= k;
 9         ++cnt;
10     }
11     return cnt;
12 }
13 int make(int a, int b, int len, int k){
14     //在k进制范围下计算构造波浪数的值
15     int x = 0, i;
16     for (i = 1; i <= len; i++){
17         if (i & 1)
18             x = x*k + a;
19         else
20             x = x*k + b;
21     }
22     return x;
23 }
24 void Search(int k){
25     int l = Len(a, k), r = Len(b, k), i, j, u;
26     //数字首位不为零，构造波浪数，减少计算次数
27     for (i = 1; i < k; i++)
28     for (j = 0; j < k; j++){
29         if (i == j) continue;
30         for (u = l; u <= r; u++){
31             int num = make(i, j, u, k);
32             if (num >= a&&num <= b) Hash[num]++;
33         }
34     }
35 }
36 int main(){
37     cin >> x >> y >> a >> b >> k;
38     for (int i = x; i <= y; i++)
39         Search(i);
40     for (int i = a; i <= b; i++)
41     if (Hash[i] == k)
42         cout << i << endl;
43     return 0;
44 }