Reverse String类型

11-23 5:40pm - 6:13pm Bobst

Reverse String

return string reversed

public String reverse(String s) {
    if(s == null || s.length() == 0) {
        return "";
    }
    StringBuilder sb = new StringBuilder();

    for(int i = s.length() - 1; i >= 0; i--) {
        sb.append(s.charAt(i));
    }

    return sb.toString();
}

Reverse Words in a String

思路就是先翻转每个word,然后在翻转整个string

比较麻烦的是处理中间多余的空格

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

        int start = 0;
        int i = 0;
        int len = s.length();

        char[] array = s.toCharArray();

        // reverse each word
        while(i < len) {
            while(i < len && s.charAt(i) == ' ') i++;
            start = i;
            while(i < len && s.charAt(i) != ' ') i++;
            reverse(array, start, i - 1);
        }

        // reverse the string
        StringBuilder sb = new StringBuilder();
        i = len - 1;
        while(i >= 0) {
            // skip the spaces
            while(i >= 0 && s.charAt(i) == ' ') i--;
            while(i >= 0 && s.charAt(i) != ' ') {
                sb.append(array[i--]);
            }
            sb.append(' ');
        }
        // remove the trailing space
        return sb.toString().trim();
    }

    private void reverse(char[] array, int start, int end) {
        for(int i = start, j = end; i < j; i++, j--) {
            char c = array[j];
            array[j] = array[i];
            array[i] = c;
        }
    }
}

Reverse Words in a String II

这一题其实是一的简化版，没有多余的空格，直接翻转就可以

public class Solution {
    public void reverseWords(char[] s) {
        if(s == null || s.length == 0) {
            return;
        }

        int start = 0;
        int i = 0;
        int len = s.length;
        // 怎么样用space来分割每个单词
        while(i < len) {
            while(i < len && s[i] != ' ') i++;
            reverse(s, start, i - 1);
            i++;
            start = i;
        }

        reverse(s, 0, len - 1);
    }

    public void reverse(char[] s, int start, int end) {
        while(start < end) {
            char temp = s[start];
            s[start] = s[end];
            s[end] = temp;
            start++;
            end--;
        }
    }
}