Day07 字符串part01| LeetCode 344. 反转字符串，541. 反转字符串II，卡码网：54.替换数字

反转字符串

344. 反转字符串

 class Solution {
        public void reverseString(char[] s) {
            int lens=s.length;
            int right,left;
            if(lens%2!=0)//奇数个
            {
                right=lens/2+1;
                left=lens/2-1;
            }
            else
            {
                right=lens/2;
                left=lens/2-1;
            }
            int i=0,j=lens-1;
            while(i<=left&&j<=lens-1)
            {
                char temp=s[i];
                s[i]=s[j];
                s[j]=temp;
                i++;
                j--;
            }

        }
    }

反转字符串II

541. 反转字符串 II

 class Solution {
        public String reverseStr(String s, int k) {
                int len=s.length();
                char[] c=s.toCharArray();
                for(int i=0;i<len;i+=2*k)
                {
                    if(i+k<=s.length())
                    {
                        reverse(c,i,i+k-1);
                    }
                    else
                    {
                        reverse(c,i,len-1);
                    }
                }
                return new String(c);
        }
        public void reverse(char[] c,int i,int j)
        {
            for(;i<j;i++,j--)
            {
                char temp=c[i];
                c[i]=c[j];
                c[j]=temp;

            }
        }
    }
  

卡码网：54.替换数字

使用额外的空间

import java.util.Scanner;

public class Main {

    public static void main(String[] args) {

        String result="";
        Scanner scanner=new Scanner(System.in);
        String s=scanner.next();

        char[] ch=s.toCharArray();
        for(int i=0;i<s.length();i++)
        {
            if(ch[i]>='a'&& ch[i]<='z')
            {
                result+=ch[i];
            }
            else
            {
                result+="number";
            }
        }
        System.out.println(result);
    }
}

不使用额外的数组空间

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String s = scanner.next();
        char[] ch = s.toCharArray();
        int count = 0;
        int OldIndex = ch.length - 1;
        
        // 统计数字字符的数量
        for (int i = 0; i < ch.length; i++) {
            if (ch[i] >= '0' && ch[i] <= '9') {
                count++;
            }
        }

        // 扩容
        char[] newS = new char[s.length() + count * 5];

        // 已扩容的下标
        int NewIndex = newS.length - 1;
        
        while (OldIndex >= 0) {
            if (ch[OldIndex] >= '0' && ch[OldIndex] <= '9') {
                newS[NewIndex--] = 'r';
                newS[NewIndex--] = 'e';
                newS[NewIndex--] = 'b';
                newS[NewIndex--] = 'm';
                newS[NewIndex--] = 'u';
                newS[NewIndex--] = 'n';
            } else {
                newS[NewIndex--] = ch[OldIndex];
            }
            OldIndex--;
        }

        System.out.println(new String(newS));
    }
}