String 字符串反转，统计次数，最大相同子串

1.字符串反转

public static void main(String[] args) {
    String s = "abcdef";
    System.out.println("原字符串  ：" + s);
    //String res = reverseString(s); 
    String res = reverseString(s, 2, 4); // 按指定角标反转
    System.out.println("反转字符串：" + res);
}

//字符串反转
public static String reverseString(String s) {
    return reverseString(s, 0, s.length());
}

//按指定角标反转
public static String reverseString(String s, int start, int end) {
    //字符串变数组
    char[] chs = s.toCharArray();
    //反转数组
    reverse(chs, start, end);
    //将数组变成字符串
    return new String(chs);
}

public static void reverse(char[] arr, int x, int y) {
    for (int start = x, end = y - 1; start < end; start++, end--) {
        swap(arr, start, end);
    }
}

public static void swap(char[] arr, int x, int y) {
    char temp = arr[x];
    arr[x] = arr[y];
    arr[y] = temp;
}

2.统计一个字符串在另一个字符串中出现的次数

public static void main(String[] args) {


    String str = "abccdefccjgeccgfc";
    String key = "cc";

    int count = getSubCount_2(str, key);
    System.out.println("count=" + count);
}


/**
 * 统计一个字符串在另一个字符串中出现的次数
 * 1，定义一个计数器
 * 2，获取key第一次出现的位置
 * 3,从第一次出现的位置后剩余的字符串中继续获取key出现的位置，每获取一次就计数一次
 * 4,当获取不到时，计数完成
 */

public static int getSubCount(String str, String key) {
    int count = 0;
    int index = 0;
    while ((index = str.indexOf(key)) != -1) {
        str = str.substring(index + key.length());
        count++;
    }
    return count;
}

public static int getSubCount_2(String str, String key) {
    int count = 0;
    int index = 0;
    while ((index = str.indexOf(key, index)) != -1) {
        System.out.println("index=" + index);
        index = index + key.length();
        count++;
    }
    return count;
}

3.获取两个字符串中最大的相同子串

public static void main(String[] args) {

    String s1 = "abchelloworld";
    String s2 = "cchellowwow";
    String maxSubString = getMaxSubString(s1, s2);
    System.out.println(maxSubString);
}

//获取两个字符串中最大的相同子串
public static String getMaxSubString(String s1, String s2) {
    String max = "";
    String min = "";
    max = (s1.length() > s2.length()) ? s1 : s2;
    min = (max == s1) ? s2 : s1;

    for (int x = 0; x < min.length(); x++) {
        for (int y = 0, z = min.length() - x; z != min.length() + 1; y++, z++) {
            String temp = min.substring(y, z);
            if (max.contains(temp)) {
                return temp;
            }
        }
    }
    return "";
}