[代码随想录] 第七天

344.翻转字符串[https://leetcode.cn/problems/reverse-string/submissions/496111203/]
思路：类似于原地翻转数组，左指针右指针向中间靠拢，交换对应元素。

class Solution {
    public void reverseString(char[] s) {
        int left=0;
        int right = s.length-1;
        char temp;
        while(right > left){
            temp=s[left];
            s[left] =s[right];
            s[right] = temp;
            left++;
            right--;
        }
    }
}

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卡码网54.替换数字[https://kamacoder.com/problempage.php?pid=1064]
思路：ez

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String s = sc.nextLine();
        StringBuilder sb = new StringBuilder();

        StringBuilder number = new StringBuilder("number");
        for (int i = 0; i < s.length(); i++) {
            if (s.charAt(i) - '0' >= 0 && s.charAt(i) - '9' <= 0) {
                sb.append(number);
            } else {
                sb.append(s.charAt(i));
            }
        }
        System.out.println(sb.toString());
    }
}

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卡码网55. 右旋字符串[https://kamacoder.com/problempage.php?pid=1065]
思路：就是将字符串分割成左右字符串，再将左字符串拼接到右字符串后。

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int k = sc.nextInt();
        sc.nextLine();
        String s = sc.nextLine();
        String temp_01 = s.substring(s.length() - k);
        String temp_02 = s.substring(0, s.length() - k);
        StringBuilder sb = new StringBuilder(temp_01);
        sb.append(temp_02);
        System.out.println(sb.toString());

    }
}

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151.翻转字符串里的单词[https://leetcode.cn/problems/reverse-words-in-a-string/description/]
思路：从右到左遍历字符串，遍历到空格时，从当前位置再往右遍历保存此单词。

class Solution {
    public String reverseWords(String s) {
        StringBuilder ans = new StringBuilder();
        int i = s.length() - 1;
        int last;
        int j;
        for (; i >= 0; i--) {
            if (s.charAt(i) != ' ') {
                last = i;
                while (i >= 0 && s.charAt(i) != ' ') {
                    i--;
                }
                j = i + 1;
                while (j <= last) {
                    ans.append(s.charAt(j));
                    j++;
                }
                ans.append(' ');
            }
        }
        ans.deleteCharAt(ans.length() - 1);
        return ans.toString();
    }
}

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541.反转字符串II[https://leetcode.cn/problems/reverse-string-ii/]
思路：难点在于right要在i+k-1和结尾中取小值！

class Solution {
    public String reverseStr(String s, int k) {
        StringBuilder sb = new StringBuilder(s);
        int right;
        int left;
        char temp;
        int loop = s.length() / k;
        for (int i = 0; i < s.length(); i += 2 * k) {
            left = i;
            right = Math.min((i + k - 1), s.length() - 1);
            while (right > left) {
                temp = sb.charAt(left);
                sb.setCharAt(left, sb.charAt(right));
                sb.setCharAt(right, temp);
                right--;
                left++;
            }
        }
        return sb.toString();
    }
}