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【Java笔记】有关String的算法题

给定一个主字符串,请返回指定字符串在主字符串中的出现次数

考点:String方法的使用

import org.junit.Test;

public class MyTest {
    public int test(String mainStr, String subStr) {
        int mainLength = mainStr.length();
        int subLength = subStr.length();
        int index = 0;
        int count = 0;//相同字符出现个数计数
        if (mainLength >= subLength) {
            while ((index = mainStr.indexOf(subStr, index)) != -1) {//indexOf返回subStr所在索引,index为从哪里开始查找
                count++;
                index += subLength;
            }
            return count;
        } else {
            return 0;
        }
    }
    @Test
    public void testGetCount(){
        String mainStr = "abdufbfabdyuabfuyirf578fab";
        String subStr = "ab";
        int cou = test(mainStr,subStr);
        System.out.println(cou);
    }
}

>>> 4

给定两个字符串,返回两个字符串中最长的相同子串,只找一次

考点:双指针与String方法的使用

import org.junit.Test;

public class MyTest {
    public String getMaxSameString(String str1, String str2){
        String maxStr = (str1.length() >= str2.length()) ? str1 : str2;
        String minStr = (str1.length() < str2.length()) ? str1 : str2;
        int length = minStr.length();//遍历多少轮
        for (int i = 0; i < length; i++) {
            for (int x = 0, y = length - i; y <= length; x++, y++) {
                String subStr = minStr.substring(x,y);
                if (maxStr.contains(subStr)){
                    return subStr;
                }
            }
        }
        return null;
    }
    @Test
    public void test(){
        String str1 = "abcdeffyubfdhello";
        String str2 = "hello";
        String str = getMaxSameString(str1,str2);
        System.out.println(str);
    }
}

>>> hello
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