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ReverseWords151.java
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ReverseWords151.java
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package Leetcode;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
public class ReverseWords151 {
/**Method1: Use Java Methods; Time: O(N); Space: O(N) **/
public String reverseWords(String s) {
s = s.trim();
List<String> words = Arrays.asList(s.split("\\s+")); //1. 空格正则\\s+
Collections.reverse(words); //2. Collections.reverse
return String.join(" ", words);
}
/**Method2: Implemented Methods; Time: O(N); Space: O(N) **/
public String reverseWords2(String s) {
StringBuilder sb = trimSpace(s);
reverse(sb, 0, sb.length() - 1);
reverseEachWords(sb);
return sb.toString();
}
private StringBuilder trimSpace(String s) {
int start = 0, end = s.length()-1;
while(start<= end && s.charAt(start) == ' ') {
start++;
}
while(start<=end && s.charAt(end) == ' ') {
end --;
}
StringBuilder sb = new StringBuilder();
while(start <= end) {
char c = s.charAt(start);
if(c != ' ' || (sb.charAt(sb.length() - 1) != ' ')){
sb.append(c);
}
start ++;
}
return sb;
}
private void reverseEachWords(StringBuilder sb){
int len = sb.length();
int start = 0;
int end = 0;
while(start < len) {
while(end < len && sb.charAt(end) != ' '){
end ++;
}
reverse(sb, start, end-1);
start = end+1;
end ++;
}
}
private void reverse(StringBuilder sb, int start, int end) {
while (start < end) {
char temp = sb.charAt(start);
sb.setCharAt(start, sb.charAt(end));
sb.setCharAt(end, temp);
start ++;
end --;
}
}
}