代码随想录Day08|字符串|344.反转字符串、541.反转字符串II、KamaCoder54.替换数字

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代码随想录开源LeetCode题单：代码随想录

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LeetCode344

LeetCode344.反转字符串

思路

双指针
定义两个指针，分别从字符串最左侧和最右侧向中间移动，同时交换元素，两指针相遇时说明反转完毕。

代码

class Solution {
    public void reverseString(char[] s) {
        int i = 0, j = s.length - 1;
        while(i < j){
            char temp = s[i];
            s[i] = s[j];
            s[j] = temp;
            i++; j--;
        }
    }
}

LeetCode541

LeetCode541.反转字符串II

数组的元素在内存地址中是连续的，不能单独删除数组中的某个元素，只能覆盖。

思路

将字符串每2k个元素分为一组，组内进行反转操作。

代码

class Solution {
    public String reverseStr(String s, int k) {
        char[] c = s.toCharArray();
        // 字符串转为字符数组后，每2k个元素分为一组，组内进行反转
        for( int i = 0; i < c.length; i += 2 * k){
            int left = i;
            int right = Math.min(c.length - 1, left + k -1);
            while(left < right){
                char temp = c[left];
                c[left] = c[right];
                c[right] = temp;
                left++;
                right--;
            }
        }
        return new String(c);
    }
}

KamaCoder54

KamaCoder54.替换数字

StringBuilder

import java.util.Scanner;

class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while(sc.hasNext()){
            StringBuilder sb = new StringBuilder();
            char[] ch = sc.nextLine().toCharArray();
            for(char c : ch) {
                if(c >= 'a' && c <= 'z') {
                    sb.append(c);
                } else {
                    sb.append("number");
                }
            }
            System.out.println(sb.toString());
        }
        return;
    }
}

扩容

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();
    }
}