# String - 186. Reverse Words in a String II

1. Reverse Words in a String II

Given an input `character array`, reverse the array word by word. A word is defined as a sequence of non-space characters.

The input character array does not contain leading or trailing spaces and the words are always separated by a single space.

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Problem Correction

### Example

Example1

``````Input: s = "the sky is blue"
Output: "blue is sky the"
``````

Example2

``````Input: "a b c"
Output: "c b a"
``````

### Challenge

Could you do it in-place without allocating extra space?

java：

``````public class Solution {
/**
* @param str: a string
* @return: return a string
*/
public char[] reverseWords(char[] str) {
if (str == null || str.length == 0) return new char[]{};

int len = str.length;
// 1. reverse whole string
reverse(str, 0, len - 1);

// 2. reverse single word
int start = 0, i = 0;
for (;i < len; i++) {
if (str[i] == ' ') {
reverse(str, start, i - 1);
start = i + 1;
}
}
reverse(str,start, i-1);

return str;
}

private void reverse(char[] s, int i, int j) {
while( i < j) {
char temp = s[i];
s[i++] = s[j];
s[j--] = temp;
}
}
}
``````

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