Invert every word in a string (should handle space)

Question

Examples:

char test1[] = " "; char test2[] = " hello z"; char test3[] = "hello world "; char test4[] = "xyz "; 

Results:

 " " " olleh z" "olleh dlrow " "xyz " 

Problem:

Flip every world in a line, ignore spaces.

Below is my code. The main idea is to scan the line when finding a word, and then cancel it. The complexity of the algorithm is O (n), where n is the length of the string.

How to check it? Is there a better solution?

 void reverse_word(char* s, char* e) { while (s < e) { char tmp = *s; *s = *e; *e = tmp; ++s; --e; } } char* word_start_index(char* p) { while ((*p != '\0') && (*p == ' ')) { ++p; } if (*p == '\0') return NULL; else return p; } char* word_end_index(char* p) { while ((*p != '\0') && (*p != ' ')) { ++p; } return p-1; } void reverse_string(char* s) { char* s_w = NULL; char* e_w = NULL; char* runner = s; while (*runner != '\0') { char* cur_word_s = word_start_index(runner); if (cur_word_s == NULL) break; char* cur_word_e = word_end_index(cur_word_s); reverse_word(cur_word_s, cur_word_e); runner = cur_word_e+1; } } 

Answer 1

Your code seems correct, but it's just C. In C ++, using the same approach, it might look something like this:

 #include <iostream> #include <string> #include <iterator> #include <algorithm> #include <cctype> int main() { std::string str = " cat cow dog wolf lobster"; std::string result; auto it = str.begin(); while (it != str.end()) { while (it != str.end() && isspace(*it)) { result += *it; ++it; } auto begin = it; while (it != str.end() && !isspace(*it)) { ++it; } auto end = it; result.append(std::reverse_iterator<decltype(end)>(end), std::reverse_iterator<decltype(begin)>(begin)); // if you want to modify original string instead, just do this: std::reverse(begin, end); } std::cout << result <<'\n'; } 

Answer 2

In place, ANSI C89.

 #include <ctype.h> #include <stdio.h> void reverse(char *s) { int i = 0, j, k; while (1) { while (isspace(s[i])) i++; if (!s[i]) return; for (j = i; !isspace(s[j]) && s[j] != '\0'; j++); for (k = 0; k < (j - i) / 2; k++) { char t = s[i + k]; s[i + k] = s[j - k - 1]; s[j - k - 1] = t; } i = j; } } int main(int argc, char**argv) { if (argc != 2) return 1; reverse(argv[1]); printf("%s\n", argv[1]); return 0; } 

Answer 3

 #include<iostream> #include<string.h> using namespace std; int main() { char s[89]; cout << "enter\n"; gets(s); int k; int p = strlen(s); strcat(s," "); for(int i=0; i <= p; i++) { if(s[i]==' ') { for (k = i-1; (k != -1) && (s[k] != ' '); k--) cout<<s[k]; cout<<" "; } } return 0; } 

Answer 4

 #include<iostream> #include<cstring> using namespace std; int main() { char str[100],a[10],s[100]=" "; int i,j; cout<<"enter a string"; cin.getline(str,100); strcat(s,str); for(i=0;s[i]!='\0';i++) { if(s[i]==' '&&s[i+1]!=' '&&s[i+1]!='\0') { cout<<" "; if(i==0)cout<<"\b"; j=i+1; while(s[j]!=' '&&s[j]!='\0') { j++; } j--; while(s[j]!=' ') { cout<<s[j]; j--; } } else if(s[i]==' ') { cout<<" "; if(i==0)cout<<"\b"; } } return 0; } 

Answer 5

 #include <iostream> #include<string.h> #include<stdio.h> using namespace std; void Reverse_Each(char st[60]) { int i,j,k=0,p=0,l; char sr[60]; l=strlen(st); for(i=0;i<=l;i++) { if((st[i]==' ')||(st[i]=='\0')) { for(j=i-1;j>=p;j--) { sr[k]=st[j]; k++; } sr[k]=' '; k++; p=i+1;} } for(i=0;i<p;i++) cout<<sr[i]; } int main(){ char s[60]; gets(s); Reverse_Each(s); return 0; }