Given three strings ‘str’, ‘oldW’ and ‘newW’. The task is find all occurrences of the word ‘oldW’ and replace then with word ‘newW’. Examples:
Input : str[] = "xxforxx xx for xx", oldW[] = "xx", newW[] = "geeks" Output : geeksforgeeks geeks for geeks
The idea is to traverse the original string and count the number of times old word occurs in the string. Now make a new string of sufficient size so that new word can be replaced. Now copy original string to new string with replacement of word.
Implementation:
// C program to search and replace // all occurrences of a word with // other word. #include <stdio.h> #include <stdlib.h> #include <string.h> // Function to replace a string with another // string char * replaceWord( const char * s, const char * oldW,
const char * newW)
{ char * result;
int i, cnt = 0;
int newWlen = strlen (newW);
int oldWlen = strlen (oldW);
// Counting the number of times old word
// occur in the string
for (i = 0; s[i] != '\0' ; i++) {
if ( strstr (&s[i], oldW) == &s[i]) {
cnt++;
// Jumping to index after the old word.
i += oldWlen - 1;
}
}
// Making new string of enough length
result = ( char *) malloc (i + cnt * (newWlen - oldWlen) + 1);
i = 0;
while (*s) {
// compare the substring with the result
if ( strstr (s, oldW) == s) {
strcpy (&result[i], newW);
i += newWlen;
s += oldWlen;
}
else
result[i++] = *s++;
}
result[i] = '\0' ;
return result;
} // Driver Program int main()
{ char str[] = "xxforxx xx for xx" ;
char c[] = "xx" ;
char d[] = "Geeks" ;
char * result = NULL;
// oldW string
printf ( "Old string: %s\n" , str);
result = replaceWord(str, c, d);
printf ( "New String: %s\n" , result);
free (result);
return 0;
} |
Old string: xxforxx xx for xx New String: GeeksforGeeks Geeks for Geeks
Time Complexity: O(n)
Auxiliary Space: O(n)
Method 2: This method involves the in-place update of the string. It is more efficient as it uses only extra space for the new characters to be inserted.
Implementation:
// C Program to replace a word in a text by another given // word by inplace updation #include <stdio.h> #include <stdlib.h> #include <string.h> void replaceWord( char * str, char * oldWord, char * newWord)
{ char *pos, temp[1000];
int index = 0;
int owlen;
owlen = strlen (oldWord);
// Repeat This loop until all occurrences are replaced.
while ((pos = strstr (str, oldWord)) != NULL) {
// Bakup current line
strcpy (temp, str);
// Index of current found word
index = pos - str;
// Terminate str after word found index
str[index] = '\0' ;
// Concatenate str with new word
strcat (str, newWord);
// Concatenate str with remaining words after
// oldword found index.
strcat (str, temp + index + owlen);
}
} int main()
{ char str[1000], oldWord[100], newWord[100];
printf ( "Enter the string: " );
gets (str);
printf ( "Enter the word to be replaced: " );
gets (oldWord);
printf ( "Replace with: " );
gets (newWord);
replaceWord(str, oldWord, newWord);
printf ( "\nModified string: %s" , str);
return 0;
} |
1 xxforxx xx for xx xx geeks
geeksforgeeks geeks for geeks
Time Complexity: O(n)
Auxiliary Space: O(1)