[Leetcode] Reverse Words in a String

最新推荐文章于 2024-01-04 11:20:32 发布

原创最新推荐文章于 2024-01-04 11:20:32 发布 · 644 阅读

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本文介绍了一种使用Java实现的方法，该方法可以将输入字符串中的单词顺序进行反转，同时处理了字符串中可能出现的多余空格问题。

Given an input string, reverse the string word by word.

For example,
Given s = "the sky is blue",
return "blue is sky the".

click to show clarification.

Clarification:

What constitutes a word?
A sequence of non-space characters constitutes a word.
Could the input string contain leading or trailing spaces?
Yes. However, your reversed string should not contain leading or trailing spaces.
How about multiple spaces between two words?
Reduce them to a single space in the reversed string.

public class Solution {
    public String reverseWords(String s) {
        if(s == null)
            return null;
        if(s.length() == 0)
            return s;
        char[] array = s.toCharArray();
        reverse(array, 0, array.length - 1);
        int index = -1;
        int start = 0;
        int space = -1;
        while(start < array.length && array[start] == ' ')
            start++;
        while(start < array.length){
            if(index == -1 || array[start] != ' ')
                array[++index] = array[start++];
            else if(array[start] == ' ' && array[index] == ' '){
                start++;
            }
            else {// array[start] == ' ' && array[index] != ' ' 
                reverse(array, space + 1, index);
                array[++index] = array[start++];
                space = index;
            }
        }
        reverse(array, space + 1, index);
        if(index == -1)
            return new String("");
        else{
            if(index < array.length && array[index] == ' ')
                return new String(array, 0, index);
            else
                return new String(array, 0, index + 1);
        }
    }
    public void reverse(char[] array, int left, int right){
        while(left < right){
            char temp = array[left];
            array[left] = array[right];
            array[right] = temp;
            left++;
            right--;
        }
    }
}

Use Java String.split()

public class Solution {
    public String reverseWords(String s) {
        if(s == null)
            return null;
        if(s.length() == 0)
            return s;
        String[] res = s.split(" ");
        StringBuilder sb = new StringBuilder("");
        for(int i = res.length - 1; i >= 0; i--)
            if(res[i].length() != 0){
                sb.append(' ');
                sb.append(res[i]);
            }
        if(sb.length() == 0)
            return sb.toString();
        return sb.substring(1, sb.length());
    }
}