longluo

/**
 * 判断数字是否是一个质数
 * 
 * check is a prime number
 * 
 */
boolean isPrime(int n) {
    for (int i = 2; i * i <= n; i++) {
        if (n % i == 0) {
            return false;

longluo

‎‎​

longluo

/**
 * Binary Search
 * 二分查找
 * 
 * Returns the index of the specified target in the specified array.
 *
 * @param arr    the array of integers, must be sorted in ascending order
 * @param target the search target
 * @return index of key in array {@code arr} if present; {@code -1} otherwise
 */

longluo

‎‎​

longluo

‎‎​

longluo

常用正则表达式

一、校验数字的表达式

1. 数字：^[0-9]*$

2. n位的数字：^\d{n}$

3. 至少n位的数字：^\d{n,}$

longluo

// KMP time: O(n+m) space: O(m)
public int KMP(String haystack, String needle) {
    if (needle == null || needle.length() == 0) {
        return 0;
    }

    int sLen = haystack.length();
    int pLen = needle.length();

    int[] next = new int[pLen];

longluo

    /**
     * The Lower 1 of the bits.
     * @param num
     * @return
     */
    public static int lowBit(int num) {
        return num & (-num);
    }

longluo

// 牛顿迭代法求某个数平方根
// Newton
public static int mySqrt_newton(int x) {
    if (x == 0) {
        return 0;
    }

    double C = x;
    double x0 = x;
    while (true) {

longluo

// GCD Recursion
public int gcd(int a, int b) {
    return b == 0 ? a : gcd(b, a % b);
}

// GCD Iteration
public int gcd_iter(int a, int b) {
    int remain = 1;
    while (remain != 0) {
        remain = a % b;