代码随想录训练营第三十期|第八天|字符串part01|344.反转字符串● 541. 反转字符串II● 卡码网：54.替换数字● 151.翻转字符串里的单词● 卡码网：55.右旋转字符串

344. 反转字符串 - 力扣（LeetCode）

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

        while (left < right) {
            char tmp = s[left];
            s[left] = s[right];
            s[right] = tmp;
            left++;
            right--;
        }

        return;
    }
}

541. 反转字符串 II - 力扣（LeetCode）

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

    private void reverse(char[] arr, int left, int right) {
        while (left < right) {
            char tmp = arr[left];
            arr[left] = arr[right];
            arr[right] = tmp;
            left++;
            right--;
        }
    }
}

151. 反转字符串中的单词 - 力扣（LeetCode）

class Solution {
    public String reverseWords(String s) {
        s = removeSpace(s);
        s = s.trim();
        if (s == null || s.length() == 0) return "";

        char[] arr = s.toCharArray();
        reverse(arr, 0, arr.length - 1);
        int start = 0;
        for (int i = 0; i < arr.length; i++) {
            if (arr[i] == ' ') continue;
            if (i == 0 || arr[i - 1] == ' ') {
                start = i;
            }
            if (i == arr.length - 1 || arr[i + 1] == ' ') {
                reverse(arr, start, i);
            }
        }
        return new String(arr);

    }

    private void reverse(char[] arr, int left, int right) {
        while (left < right) {
            char tmp = arr[left];
            arr[left] = arr[right];
            arr[right] = tmp;
            left++;
            right--;
        }
    }

    private String removeSpace(String s) {
        StringBuilder sb = new StringBuilder();
        int start = 0;
        for (int i = 0; i < s.length(); i++) {
            if (s.charAt(i) == ' ') continue;
            if (i == 0 || s.charAt(i - 1) == ' ') {
                start = i;
            }
            if (i == s.length() - 1 || s.charAt(i + 1) == ' ') {
                sb.append(s.substring(start, i + 1)).append(' ');
            }
        }
        return sb.toString();
    }
}