Algorithm
Problem Name: 344. Reverse String
Problem URL: https://leetcode.com/problems/reverse-string/
Level: Easy
Details:
Write a function that reverses a string. The input string is given as an array of characters s.
You must do this by modifying the input array in-place with O(1) extra memory.
Example 1:
Input: s = ["h","e","l","l","o"] Output: ["o","l","l","e","h"]
Example 2:
Input: s = ["H","a","n","n","a","h"] Output: ["h","a","n","n","a","H"]
Constraints:
1 <= s.length <= 105s[i]is a printable ascii character.
Algorithm:
We can solve this Reverse String problem in several ways.
Method 1: Use javascript reverse() method to reverse any string.
array.reverse();
Method 2: Using forEach or for loop to solve the problem.
We can start the loop from end to start.
const reversed = [];
for(let i = s.length - 1; i >= 0; i--) {
reversed.push(s[i]);
}
s.forEach((ch, i) => {
s[i] = reversed[i];
});Code Examples
#1 Code Example with Javascript Programming
Code -
Javascript Programming
var reverseString = function(s) {
return s.reverse();
};
Input
Output
#2 Using For Loop to solve Reverse problem in Javascript [Not tested]
Code -
Javascript Programming
var reverseString = function(s) {
const reversed = [];
for(let i = s.length - 1; i >= 0; i--) {
reversed.push(s[i]);
}
s.forEach((ch, i) => {
s[i] = reversed[i];
});
};
Input
Output
#3 Code Example with C Programming
Code -
C Programming
char* reverseString(char* s) {
int i = 0;
int j;
char c;
if (!s) return s;
j = strlen(s);
if (j < 2) return s;
j --;
while (i < j) {
c = s[j];
s[j] = s[i];
s[i] = c;
i ++;
j --;
}
return s;
}
Input
Output
#3 Code Example with C Programming
Code -
C Programming
char* reverseString(char* s) {
int i = 0;
int j;
char c;
if (!s) return s;
j = strlen(s);
if (j < 2) return s;
j --;
while (i < j) {
c = s[j];
s[j] = s[i];
s[i] = c;
i ++;
j --;
}
return s;
}
Input
Output
#3 Code Example with C Programming
Code -
C Programming
char* reverseString(char* s) {
int i = 0;
int j;
char c;
if (!s) return s;
j = strlen(s);
if (j < 2) return s;
j --;
while (i < j) {
c = s[j];
s[j] = s[i];
s[i] = c;
i ++;
j --;
}
return s;
}
Input
Output
#4 Code Example with C++ Programming
Code -
C++ Programming
class Solution {
public:
string reverseString(string s) {
reverse(s.begin(), s.end());
return s;
}
};
Input
Output
#4 Code Example with C++ Programming
Code -
C++ Programming
class Solution {
public:
string reverseString(string s) {
reverse(s.begin(), s.end());
return s;
}
};
Input
Output
#4 Code Example with C++ Programming
Code -
C++ Programming
class Solution {
public:
string reverseString(string s) {
reverse(s.begin(), s.end());
return s;
}
};
Input
Output
#5 Code Example with C# Programming
Code -
C# Programming
namespace LeetCode
{
public class _0344_ReverseString
{
public void ReverseString(char[] s)
{
if (s == null || s.Length == 0) return;
int i = 0, j = s.Length - 1;
while (i < j)
{
var temp = s[i];
s[i] = s[j];
s[j] = temp;
i++; j--;
}
}
}
}
Input
Output
#5 Code Example with C# Programming
Code -
C# Programming
namespace LeetCode
{
public class _0344_ReverseString
{
public void ReverseString(char[] s)
{
if (s == null || s.Length == 0) return;
int i = 0, j = s.Length - 1;
while (i < j)
{
var temp = s[i];
s[i] = s[j];
s[j] = temp;
i++; j--;
}
}
}
}
Input
Output
#5 Code Example with C# Programming
Code -
C# Programming
namespace LeetCode
{
public class _0344_ReverseString
{
public void ReverseString(char[] s)
{
if (s == null || s.Length == 0) return;
int i = 0, j = s.Length - 1;
while (i < j)
{
var temp = s[i];
s[i] = s[j];
s[j] = temp;
i++; j--;
}
}
}
}
Input
Output
#6 Code Example with Java Programming
Code -
Java Programming
class Solution {
public void reverseString(char[] s) {
int start = 0;
int end = s.length - 1;
while (start < end) {
char temp = s[start];
s[start++] = s[end];
s[end--] = temp;
}
}
}
Input
Output
#6 Code Example with Java Programming
Code -
Java Programming
class Solution {
public void reverseString(char[] s) {
int start = 0;
int end = s.length - 1;
while (start < end) {
char temp = s[start];
s[start++] = s[end];
s[end--] = temp;
}
}
}
Input
Output
#6 Code Example with Java Programming
Code -
Java Programming
class Solution {
public void reverseString(char[] s) {
int start = 0;
int end = s.length - 1;
while (start < end) {
char temp = s[start];
s[start++] = s[end];
s[end--] = temp;
}
}
}
Input
Output
#7 Code Example with Python Programming
Code -
Python Programming
class Solution:
def reverseString(self, s: List[str]) -> None:
"""
Do not return anything, modify s in-place instead.
"""
for i in range(len(s) // 2):
s[i], s[-i-1] = s[-i-1], s[i]
Input
Output
#7 Code Example with Python Programming
Code -
Python Programming
class Solution:
def reverseString(self, s: List[str]) -> None:
"""
Do not return anything, modify s in-place instead.
"""
for i in range(len(s) // 2):
s[i], s[-i-1] = s[-i-1], s[i]
Input
Output
#7 Code Example with Python Programming
Code -
Python Programming
class Solution:
def reverseString(self, s: List[str]) -> None:
"""
Do not return anything, modify s in-place instead.
"""
for i in range(len(s) // 2):
s[i], s[-i-1] = s[-i-1], s[i]
Input
Output
Demonstration
We'll just use string reverse() method of javascript.
Leetcode - 344. Reverse String Solution in Javascript Leetcode