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  • Reverse Words in a String

    题目:

    Given an input string s, reverse the string word by word.
    For example, given s = "the sky is blue", return "blue is sky the"

    Example Questions Candidate Might Ask:
    Q: What constitutes a word?
    A: A sequence of non-space characters constitutes a word.
    Q: Does tab or newline character count as space characters?
    A: Assume the input does not contain any tabs or newline characters.
    Q: Could the input string contain leading or trailing spaces?
    A: Yes. However, your reversed string should not contain leading or trailing spaces.
    Q: How about multiple spaces between two words?
    A: Reduce them to a single space in the reversed string.

    解答:

     1 public String reverseWords(String s) {
     2 
     3     StringBuilder reversed = new StringBuilder();
     4     int j = s.length();
     5 
     6     for(int i = s.length()-1; i >= 0; i--) {
     7         if(s.charAt(i) == ' ') {
     8             j = i;
     9         } else if(i == 0 || s.charAt(i-1) == ' ') {
    10             if(reversed.length() != 0) {
    11                 reversed.append(' ');
    12             }
    13 
    14             reversed.append(s.substring(i, j));
    15         }
    16     }
    17 
    18     return reversed.toString();
    19 }

    如果如何只允许使用O(1)的额外空间呢?

     1 public void reverseWords(char[] s) {
     2     reverse(s, 0, s.length);
     3     for(int i = 0, j = 0; j <= s.length; j++) {
     4         if(j == s.length() || s[j] == ' ') {
     5             reverse(s, i, j);
     6             i = j + 1;
     7         }
     8     }
     9 }
    10 
    11 public void reverse(char[] s, int begin, int end) {
    12     for(int i = 0; i < (end - begin) >> 1; i++) {
    13         char tmp = s[begin + i];
    14         s[begin + i] = s[end -1 - i];
    15         s[end -1 - i] = tmp;
    16     }
    17 }
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  • 原文地址:https://www.cnblogs.com/wylwyl/p/10348414.html
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