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

For example,

Given s = "the sky is blue",

return "blue is sky the".

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解题思路：

用trim() 和splite("\\s+")把String 切割成一个一个word, 然后用StringBuilder 重建String. O(n) time and O(n) Space

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Java code:

public String reverseWords(String s) {        if( s == null || s.length() == 0 ){            return "";        }        String[] splited = s.trim().split("\\s+");        int len = splited.length;        StringBuilder sb = new StringBuilder();        for(int i = len-1; i >= 0; i--){            sb.append(splited[i] + " ");        }        return sb.toString().trim();    }

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Reference:

1. https://leetcode.com/discuss/56712/straightforward-java-solution-using-split