String Reverse In-place
Easy
C
Strings
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Problem Statement
Reverse a string without extra arrays. Two pointer technique: swap characters from the start and end until they meet in the middle.
Input Format
A string entered by the user.
Output Format
The same string reversed in-place.
Example
"computer"
"retupmoc"
Constraints
• No extra array allowed
• In-place modification only
• In-place modification only
Concept Explanation
The string is reversed by swapping characters from the start and end using two pointers.
Step-by-Step Explanation
1.Take the input string.
2.Set pointer start at the first character.
3.Set pointer end at the last character.
4.While start < end:
5.Swap characters at start and end.
6.Move start one step forward.
7.Move end one step backward.
8.Stop when both pointers meet.
9.The string is reversed in the same memory.
2.Set pointer start at the first character.
3.Set pointer end at the last character.
4.While start < end:
5.Swap characters at start and end.
6.Move start one step forward.
7.Move end one step backward.
8.Stop when both pointers meet.
9.The string is reversed in the same memory.
Concept Explanation
The string is reversed by swapping characters from the start and end using two pointers.
Step-by-Step Explanation
1.Take the input string.
2.Set pointer start at the first character.
3.Set pointer end at the last character.
4.While start < end:
5.Swap characters at start and end.
6.Move start one step forward.
7.Move end one step backward.
8.Stop when both pointers meet.
9.The string is reversed in the same memory.
2.Set pointer start at the first character.
3.Set pointer end at the last character.
4.While start < end:
5.Swap characters at start and end.
6.Move start one step forward.
7.Move end one step backward.
8.Stop when both pointers meet.
9.The string is reversed in the same memory.
Input / Output Format
Input Format
A string entered by the user.
Output Format
The same string reversed in-place.
Constraints
• No extra array allowed
• In-place modification only
• In-place modification only
Examples
Input:
"computer"
Output:
"retupmoc"
Example Solution (Public)
#include <stdio.h>
int main() {
char str[100];
int start = 0, end, i;
char temp;
printf("Enter a string: ");
fgets(str, sizeof(str), stdin);
// Find length manually
end = 0;
while (str[end] != '�') {
end++;
}
// Remove newline if present
if (str[end - 1] == 'n') {
end--;
}
end = end - 1; // index of last character
// Two-pointer swap
while (start < end) {
temp = str[start];
str[start] = str[end];
str[end] = temp;
start++;
end--;
}
printf("Reversed string: %sn", str);
return 0;
}
Official Solution Code
#include <stdio.h>
int main() {
char str[100];
int start = 0, end, i;
char temp;
printf("Enter a string: ");
fgets(str, sizeof(str), stdin);
// Find length manually
end = 0;
while (str[end] != '�') {
end++;
}
// Remove newline if present
if (str[end - 1] == 'n') {
end--;
}
end = end - 1; // index of last character
// Two-pointer swap
while (start < end) {
temp = str[start];
str[start] = str[end];
str[end] = temp;
start++;
end--;
}
printf("Reversed string: %sn", str);
return 0;
}
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