344.反转字符串
力扣题目链接：. - 力扣（LeetCode）
双指针
class Solution {public void reverseString(char[] s) {int leftindex=0;int rightindex=s.length-1;while(leftindex<rightindex){char temp=s[leftindex];s[leftindex]=s[rightindex];s[rightindex]=temp;leftindex++;rightindex--;}}
}541. 反转字符串II
力扣题目链接：. - 力扣（LeetCode）
双指针
class Solution {public String reverseStr(String s, int k) {char[] sarray=s.toCharArray();for(int i=0;i<sarray.length;i+=2*k){int start=i;int end=Math.min(sarray.length-1,i+k-1);while(start<end){char temp=sarray[start];sarray[start]=sarray[end];sarray[end]=temp;start++;end--;}}return new String(sarray);}
}卡码网：54.替换数字
卡码题目链接：54. 替换数字（第八期模拟笔试）
import java.util.Scanner;public class Main {public static String replaceNumber(String s) {int count = 0; // 统计数字的个数int sOldSize = s.length();for (int i = 0; i < s.length(); i++) {if(Character.isDigit(s.charAt(i))){count++;}}// 扩充字符串s的大小，也就是每个空格替换成"number"之后的大小char[] newS = new char[s.length() + count * 5];int sNewSize = newS.length;// 将旧字符串的内容填入新数组System.arraycopy(s.toCharArray(), 0, newS, 0, sOldSize);// 从后先前将空格替换为"number"for (int i = sNewSize - 1, j = sOldSize - 1; j < i; j--, i--) {if (!Character.isDigit(newS[j])) {newS[i] = newS[j];} else {newS[i] = 'r';newS[i - 1] = 'e';newS[i - 2] = 'b';newS[i - 3] = 'm';newS[i - 4] = 'u';newS[i - 5] = 'n';i -= 5;}}return new String(newS);};public static void main(String[] args) {Scanner scanner = new Scanner(System.in);String s = scanner.next();System.out.println(replaceNumber(s));scanner.close();}
}