1059. Prime Factors

筛素数法，分解因式

// 1059_Prime_Factors.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <stdio.h>
#include <math.h>

const int N = 31650;
bool prime[N];

void selectPrime(){
	prime[0] = prime[1] = true;
	for(int i = 2; i < N; i++){
		if(!prime[i]){
			for(int j = i * i; j < N; j += i){
				prime[j] = true;
			}
		}
	}
}

void countYue(int num){
	int tNum = num;
	printf("%d=", num);
	if(num == 1){
		printf("1\n");
		return;
	}
	bool tag = true;
	int tn = (int)sqrt(1.0 * num);
	for(int i = 2; i <= tn; i++){
		if(num == 1)
			break;
		if(!prime[i]){
			int tCnt = 0;
			while(num % i ==0){
				++tCnt;
				num = num / i;
			}
			if(tCnt != 0){
				if(tag)
					tag = false;
				else
					printf("*");
				printf("%d",i);
				if(tCnt != 1)
					printf("^%d", tCnt);
			}
		}
	}
	if(num != 1){
		if(num == tNum)
			printf("%d\n", num);
		else
			printf("*%d\n", num);
	}
	else
		printf("\n");
}

int main(int argc, char* argv[])
{
	int num;
	while(~scanf("%d", &num)){
		selectPrime();
		countYue(num);
	}
	return 0;
}