题意:给定三个数a、b、c,构造一个序列,这个序列的元素的质因数只能是a或b或c,求这个序列的第n个数。
另外两道题的思路几乎相同:1338:因子只能是2、3或5;
2591:如果x在序列里,那么2x+1和3x+1一定在。
思路:通过下标进行枚举。
2545代码:
#include <cstdio> #include <cstring> #include <algorithm> using namespace std; #define clr(s,t) memset(s,t,sizeof(s)) int a,b,c,n; long long s[10000]; int main(){ int i,ia,ib,ic; long long k; scanf("%d %d %d %d",&a,&b,&c,&n); s[1] = ia = ib = ic = 1; for(i = 1;i<=n;i++){ k = min(min(s[ia]*a, s[ib]*b), s[ic]*c); s[i+1] = k; if(k == s[ia]*a) ia++; if(k == s[ib]*b) ib++; if(k == s[ic]*c) ic++; } printf("%lld\n",k); return 0; }
#include <stdio.h> int s[1502]; int main() { int min(int x,int y,int z); int i2,i3,i5; int i; int n; i2 = i3 = i5 = 1; s[1] = 1; for(i = 2;i<=1500;i++){ s[i] = min(s[i2]*2,s[i3]*3,s[i5]*5); if(s[i] == s[i2]*2) i2++; if(s[i] == s[i3]*3) i3++; if(s[i] == s[i5]*5) i5++; } while(scanf("%d",&n)&&n){ printf("%d\n",s[n]); } } int min(int x,int y,int z){ x = x < y ? x : y; x = x < z ? x : z; return x; }
2591代码:
#include <stdio.h> int s[10000002]; int main() { int a,b; int n; int i = 1; a = b = 1; s[1] = 1; while(++i<=10000000){ if(2*s[a]+1 < 3*s[b]+1){ s[i] = 2*s[a]+1; a++; } else if(2*s[a]+1 > 3*s[b]+1){ s[i] = 3*s[b]+1; b++; } else{ s[i] = 2*s[a]+1; a++; b++; } } while(scanf("%d",&n)!=EOF){ printf("%d\n",s[n]); } }