LeetCode刷题Day08——字符串（字符串交换）

/**
 * <pre>
 * 双指针指向头和尾，不断交换并向中间靠拢 
 * </pre>
 *
 * @author <a href="https://github.com/Ken-Chy129">Ken-Chy129</a>
 * @date 2023/1/9 11:06
 */
public class 反转字符串344 {
    public void reverseString(char[] s) {
        int len = s.length;
        char tmp;
        for (int i=0; i<len/2; i++) {
            tmp = s[len-i-1];
            s[len-i-1] = s[i];
            s[i] = tmp;
        }
    }
}

/**
 * <pre>
 * 每隔k个反转k个，末尾不够k个时全部反转
 * </pre>
 *
 * @author <a href="https://github.com/Ken-Chy129">Ken-Chy129</a>
 * @date 2023/1/9 11:16
 */
public class 反转字符串II541 {
    public String reverseStr(String s, int k) {
        char[] chars = s.toCharArray();
        for (int i=0; i<s.length(); i+=2*k) {
            reserve(chars, i, Math.min(i + k, s.length()));
        }
        return new String(chars);
    }
    public void reserve(char[] chars, int begin, int end) {
        int len = end - begin;
        char tmp;
        for (int i=0; i<len/2; i++) {
            tmp = chars[end-i-1];
            chars[end-i-1] = chars[begin+i];
            chars[begin+i] = tmp;
        }
    }
}

public class 替换空格5 {
    public String replaceSpace(String s) {
        StringBuilder sb = new StringBuilder();
        for (int i=0; i<s.length(); i++) {
            if (s.charAt(i) == ' ') {
                sb.append('%');
                sb.append('2');
                sb.append('0');
            } else {
                sb.append(s.charAt(i));
            }
        }
        return sb.toString();
    }
}

/**
 * <pre>
 * 1.用栈维护
 * 2.调用api
 * </pre>
 *
 * @author <a href="https://github.com/Ken-Chy129">Ken-Chy129</a>
 * @date 2023/1/9 13:57
 */
public class 反转字符串中的单词151 {
    // 用栈维护
    public String reverseWords(String s) {
        int i = 0, len = s.length();
        Stack<String> stack = new Stack<>();
        while (i<len) {
            while (i < len && s.charAt(i) == ' ') {
                i++;
            }
            if (i == len) {
                break;
            }
            StringBuilder sb = new StringBuilder();
            while (i < len && s.charAt(i) != ' ') {
                sb.append(s.charAt(i++));
            }
            stack.add(sb.toString());
        }
        StringBuilder res = new StringBuilder();
        while (stack.size() > 1) {
            res.append(stack.pop());
            res.append(' ');
        }
        res.append(stack.pop());
        return res.toString();
    }
    // 调用api
    public String reverseWords2(String s) {
        // 除去开头和末尾的空白字符
        s = s.trim();
        // 正则匹配连续的空白字符作为分隔符分割
        List<String> wordList = Arrays.asList(s.split("\\s+"));
        Collections.reverse(wordList);
        return String.join(" ", wordList);
    }
}