string 反转字符串中单词的顺序
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Reverse the ordering of words in a string
提问by Arnkrishn
I have this string s1 = "My name is X Y Z"and I want to reverse the order of the words so that s1 = "Z Y X is name My".
我有这个string s1 = "My name is X Y Z"，我想颠倒单词的顺序，以便s1 = "Z Y X is name My".
I can do it using an additional array. I thought hard but is it possible to do it inplace (without using additional data structures) and with the time complexity being O(n)?
我可以使用额外的数组来做到这一点。我想得很努力，但是否有可能就地进行（不使用额外的数据结构）并且时间复杂度为 O(n)？
回答by Bill the Lizard
Reverse the entire string, then reverse the letters of each individual word.
反转整个字符串，然后反转每个单词的字母。
After the first pass the string will be
第一次通过后，字符串将是
s1 = "Z Y X si eman yM"
and after the second pass it will be
在第二遍之后，它将是
s1 = "Z Y X is name My"
回答by Demi
reverse the string and then, in a second pass, reverse each word...
反转字符串，然后在第二遍中反转每个单词...
in c#, completely in-place without additional arrays:
在 c# 中，完全就地，无需额外的数组：
static char[] ReverseAllWords(char[] in_text)
{
int lindex = 0;
int rindex = in_text.Length - 1;
if (rindex > 1)
{
//reverse complete phrase
in_text = ReverseString(in_text, 0, rindex);
//reverse each word in resultant reversed phrase
for (rindex = 0; rindex <= in_text.Length; rindex++)
{
if (rindex == in_text.Length || in_text[rindex] == ' ')
{
in_text = ReverseString(in_text, lindex, rindex - 1);
lindex = rindex + 1;
}
}
}
return in_text;
}
static char[] ReverseString(char[] intext, int lindex, int rindex)
{
char tempc;
while (lindex < rindex)
{
tempc = intext[lindex];
intext[lindex++] = intext[rindex];
intext[rindex--] = tempc;
}
return intext;
}
回答by Demi
Not exactly in place, but anyway: Python:
>>> a = "These pretzels are making me thirsty"
>>> " ".join(a.split()[::-1])
'thirsty me making are pretzels These'
回答by Wrameerez
In Smalltalk:
在 Smalltalk 中：
'These pretzels are making me thirsty' subStrings reduce: [:a :b| b, ' ', a]
I know noone cares about Smalltalk, but it's so beautiful to me.
我知道没有人关心 Smalltalk，但它对我来说太美妙了。
回答by baumgart
You cannot do the reversal without at least some extra data structure. I think the smallest structure would be a single character as a buffer while you swap letters. It can still be considered "in place", but it's not completely "extra data structure free".
如果没有至少一些额外的数据结构，您就无法进行逆转。我认为在交换字母时，最小的结构是单个字符作为缓冲区。它仍然可以被认为是“就地”，但它并不是完全“没有额外的数据结构”。
Below is code implementing what Bill the Lizard describes:
下面是实现蜥蜴比尔描述的代码：
string words = "this is a test";
// Reverse the entire string
for(int i = 0; i < strlen(words) / 2; ++i) {
char temp = words[i];
words[i] = words[strlen(words) - i];
words[strlen(words) - i] = temp;
}
// Reverse each word
for(int i = 0; i < strlen(words); ++i) {
int wordstart = -1;
int wordend = -1;
if(words[i] != ' ') {
wordstart = i;
for(int j = wordstart; j < strlen(words); ++j) {
if(words[j] == ' ') {
wordend = j - 1;
break;
}
}
if(wordend == -1)
wordend = strlen(words);
for(int j = wordstart ; j <= (wordend + wordstart) / 2 ; ++j) {
char temp = words[j];
words[j] = words[wordend - (j - wordstart)];
words[wordend - (j - wordstart)] = temp;
}
i = wordend;
}
}
回答by Alex S
What language? If PHP, you can explode on space, then pass the result to array_reverse.
什么语言？如果是 PHP，则可以在空间上爆炸，然后将结果传递给 array_reverse。
If its not PHP, you'll have to do something slightly more complex like:
如果它不是 PHP，你将不得不做一些稍微复杂的事情，比如：
words = aString.split(" ");
for (i = 0; i < words.length; i++) {
words[i] = words[words.length-i];
}
回答by Alex S
public static String ReverseString(String str)
{
int word_length = 0;
String result = "";
for (int i=0; i<str.Length; i++)
{
if (str[i] == ' ')
{
result = " " + result;
word_length = 0;
} else
{
result = result.Insert(word_length, str[i].ToString());
word_length++;
}
}
return result;
}
This is C# code.
这是 C# 代码。
回答by Kaymatrix
In Python...
ip = "My name is X Y Z"
words = ip.split()
words.reverse()
print ' '.join(words)
Anyway cookamunga provided good inline solution using python!
不管怎样，cookamunga 使用 python 提供了很好的内联解决方案！
回答by Nikola Mitev
class Program
{
static void Main(string[] args)
{
string s1 =" My Name varma:;
string[] arr = s1.Split(' ');
Array.Reverse(arr);
string str = string.Join(" ", arr);
Console.WriteLine(str);
Console.ReadLine();
}
}
回答by AbhinavChoudhury
This is assuming all words are separated by spaces:
这是假设所有单词都用空格分隔：
#include <stdio.h>
#include <string.h>
int main()
{
char string[] = "What are you looking at";
int i, n = strlen(string);
int tail = n-1;
for(i=n-1;i>=0;i--)
{
if(string[i] == ' ' || i == 0)
{
int cursor = (i==0? i: i+1);
while(cursor <= tail)
printf("%c", string[cursor++]);
printf(" ");
tail = i-1;
}
}
return 0;
}
