求最大公约数

// 从小到大
public static int gcd(int m, int n) {

        int gcd = 1;
        for (int i = 2; i <= m && i <= n; i++) {
            if (m % i == 0 && n % i == 0) {
                gcd = i;
            }
        }
        return gcd;
    }

// 从大到小
public static int gcd(int m, int n) {

int gcd = 1;
        for (int i = n; i >= 1; i--) {
            if (m % i == 0 && n % i == 0) {
                gcd = i;
                break;
            }
        }
        return gcd;
    }

// 穷举算法  数字n的除数不可能比n/2大
public static int gcd(int m, int n) {

        int gcd = 1;
        if (m % n == 0) {
            return n;
        }
        for (int i = n / 2; i >= 1; i--) {
            if (m % i == 0 && n % i == 0) {
                gcd = i;
                break;
            }
        }
        return gcd;
    }

public static int gcd(int m, int n) {

        if (m % n == 0) {
            return n;
        }
        else {
            return gcd(n, m % n);
        }
    }

public static int gcd(int m, int n) {

        int remainder = m % n;
        while (remainder > 0) {
            m = n;
            n = remainder;
            remainder = m % n;
        }
        return n;
    }