n! 多少个0

/** * n! 多少个0 * 实际就是5的个数 */public class Zero {public static int count(int n){if(n < 1){return -1;}int count = 0;for(int i=1; i<=n; i++){int m = i;while(m%5 == 0){count++;m = m/5;}}return count;}public static int count2(int n){if(n < 1){return -1;}int count = 0;while(n>0){int m = n;while(m%5 == 0){count++;m = m/5;}n--;}return count;}public static int count3(int n){if(n < 1){return -1;}int count = 0;while(n > 0){count += n/5;n = n/5;}return count;}public static long by(int n){long m = 1;while(n>0){n--;m *= (n+1)*n;n--;}return m;}/** * @param args */public static void main(String[] args) {int count = Zero.count(10);int count2 = Zero.count2(10);int count3 = Zero.count2(10);long number = Zero.by(10);System.out.println(number);System.out.println(count);System.out.println(count2);System.out.println(count3);}}