Number theory-prime number

1:3 Basic prime-number judgments

1: Exhaustive method: Suitable for when the data is small. Complexity of Time: O ()

intIsPrime (intN) {    if(n==1|| n==0)        return 0; intm = sqrt (n+0.5);  for(inti =2; I <= m; i++)        if(n%i==0)            return 0; return 1;}

2: Elatosseni Sieve method to calculate the time complexity of prime number: O ()

#include <cmath>#include<cstdio>#include<cstring>#include<iostream>#include<algorithm>using namespacestd;Const intMAXN =1e6;intBOOK[MAXN];intPRIME[MAXN];intMainvoid){    intN; intnum;  while(~SCANF ("%d",&N)) {num=0;  for(inti =2; I <= N; i++)        {            if(book[i]==0) Prime[num++] =i;  for(intj = i * I; J <= N; J + =i) {book[j]=1; }        }                 for(inti =0; i < num; i++) cout<<prime[i]<<Endl; }    return 0;}

3: Euler Sieve method

#include <cmath>#include<cstdio>#include<cstring>#include<iostream>#include<algorithm>using namespacestd;Const intMAXN =1e6;intPRIME[MAXN];intBOOK[MAXN];intMainvoid){    intN; intnum;  while(~SCANF ("%d", &N)) {num=0;  for(inti =2; I <= N; i++)        {            if(book[i]==0) Prime[num++] =i;  for(intj =0; J < num; J + +)            {                if(I*prime[j] >N) Break;//jump out when you are too bigBOOK[I*PRIME[J]] =1; if((i%prime[j]) = =0)//If I is a composite, and I% prime[j] = = 0                     Break; }        }         for(inti =0; i < num; i++) printf ("%d\n", Prime[i]); }    return 0;}

Number theory-prime number