Interview questions:
1. Simulate a trim method to remove the spaces at both ends of the string.
2. Reverse a character string. Reverse the specified part of the string. For example, "abcdefg" is reversed to "abfedcg".
//将一个字符串进行反转。将字符串中指定部分进行反转。比如“abcdefg”反转为“abfedcg”。
public class ReverseTest {
@Test
public void test() {
String str = "abcdefg";
String r = reverse(str, 2, 5);
System.out.println(r);
}
//方式一：转换为char[]
public String reverse(String str, int startIndex, int endIndex) {
if (str != null ) {
char[] c = str.toCharArray();
for (int x = startIndex, y = endIndex; x < y; x++, y--) {
char temp = c[x];
c[x] = c[y];
c[y] = temp;
}
return new String(c);
}
return null;
}
//方式二：使用String拼接
public String reverse1(String str, int startIndex, int endIndex) {
if (str != null) {
//第一部分
String reverseStr = str.substring(0, startIndex);
//第二部分
for (int i = startIndex; i >= startIndex; i--) {
reverseStr += str.charAt(i);
}
//第三部分
reverseStr += str.substring(endIndex + 1);
return reverseStr;
}
return null;
}
}
3. Get the number of occurrences of a string in another character. (For example: get the number of occurrences of "ab" in "abkkcadkabkekafkabkskab").
/*
* 获取一个字符串在另一个字符串中出现的次数。
* 比如：获取“ab”在“abkkcadkabkebfkaabkskab”中出现的次数
*/
public class FindTest {
public int getCount(String mainStr,String subStr){
int mainLength = mainStr.length();
int subLength = subStr.length();
int count = 0;
int index = 0;
if (mainLength >= subLength){
while ((index = mainStr.indexOf(subStr,index)) != -1){
count++;
index += subLength;
}
return count;
}else {
return 0;
}
}
@Test
public void test(){
String mainStr = "abkkcadkabkebfkaabkskab";
String subStr = "ab";
int count = getCount(mainStr,subStr);
System.out.println(count);
}
}
4. Get the largest identical substring in the two strings. For example: str1 = "abcwerthellotuiodef"; str2 = "cvhellobnm". Hint: Compare the shorter string with the longer string with decreasing length.
/*
* 获取两个字符串中最大相同子串。比如：
* str1="abcwerthelloyuiodef";str2="cvhellobnm"
* 提示：将短的那个串进行长度依次递减的子串与较长的串比较。
*/
public class MaxSameTest {
/*//前提：字符串中只有一个最大相同值
public String getMaxSameSubString(String str1, String str2) {
if (str1 != null && str2 != null){
String maxStr = str1.length() >= str2.length() ? str1 : str2;
String minStr = str1.length() < str2.length() ? str1 : str2;
int length = minStr.length();
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;
}*/
//情况：字符串中有多个相同串
public String[] getMaxSameSubString1(String str1, String str2) {
if (str1 != null && str2 != null) {
StringBuffer sBuffer = new StringBuffer();
String maxString = (str1.length() >= str2.length()) ? str1 : str2;
String minString = (str1.length() < str2.length()) ? str1 : str2;
int len = minString.length();
for (int i = 0; i < len; i++) {
for (int x = 0, y = len - i; y <= len; x++, y++) {
String subString = minString.substring(x, y);
if (maxString.contains(subString)) {
sBuffer.append(subString + ",");
}
}
// System.out.println(sBuffer);
if (sBuffer.length() != 0) {
break;
}
}
String[] split = sBuffer.toString().replaceAll(",$", "").split("\\,");
return split;
}
return null;
}
@Test
public void test() {
String str1 = "abcwerthello1yuiodefabcdef";
String str2 = "cvhello1bnmabcdef";
String[] maxSameSubStrings = getMaxSameSubString1(str1, str2);
System.out.println(Arrays.toString(maxSameSubStrings));
}
}
5. Sort the characters in the string in natural order. Tips: ①The string becomes an array of characters. ② Sort the array, select, bubble, Arrays.sort(); ③ Turn the sorted array into a string.