151.reverse-words-in-a-string.java

/*
 * [151] Reverse Words in a String
 *
 * https://leetcode.com/problems/reverse-words-in-a-string/description/
 *
 * algorithms
 * Medium (15.70%)
 * Total Accepted:    182.8K
 * Total Submissions: 1.2M
 * Testcase Example:  '""'
 *
 * 
 * Given an input string, reverse the string word by word.
 * 
 * 
 * 
 * For example,
 * Given s = "the sky is blue",
 * return "blue is sky the".
 * 
 * 
 * 
 * Update (2015-02-12):
 * For C programmers: Try to solve it in-place in O(1) space.
 * 
 * 
 * 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) {
		int j = s.length();
		StringBuilder sb = new StringBuilder();
		for (int i = s.length() - 1; i >= 0; i--) {
			if (s.charAt(i) == ' ') {
				j = i;
			} else {
				if (i == 0 || s.charAt(i - 1) == ' ') {
					if (sb.length() != 0) {
						sb.append(" ");
					}
					sb.append(s.substring(i, j));
				}
			}
		}		

		return sb.toString();
    }
}