Find last index of a character in a string
Last Updated :
27 Jul, 2022
Given a string str and a character x, find last index of x in str.
Examples :
Input : str = "geeks", x = 'e'
Output : 2
Last index of 'e' in "geeks" is: 2
Input : str = "Hello world!", x = 'o'
Output : 7
Last index of 'o' is: 7
Method 1 (Simple : Traverse from left): Traverse given string from left to right and keep updating index whenever x matches with current character.
Implementation:
C++
// CPP program to find last index of
// character x in given string.
#include <iostream>
using namespace std;
// Returns last index of x if it is present.
// Else returns -1.
int findLastIndex(string& str, char x)
{
int index = -1;
for (int i = 0; i < str.length(); i++)
if (str[i] == x)
index = i;
return index;
}
// Driver code
int main()
{
// String in which char is to be found
string str = "geeksforgeeks";
// char whose index is to be found
char x = 'e';
int index = findLastIndex(str, x);
if (index == -1)
cout << "Character not found";
else
cout << "Last index is " << index;
return 0;
}
// Java program to find last index
// of character x in given string.
import java.io.*;
class GFG {
// Returns last index of x if
// it is present Else returns -1.
static int findLastIndex(String str, Character x)
{
int index = -1;
for (int i = 0; i < str.length(); i++)
if (str.charAt(i) == x)
index = i;
return index;
}
// Driver code
public static void main(String[] args)
{
// String in which char is to be found
String str = "geeksforgeeks";
// char whose index is to be found
Character x = 'e';
int index = findLastIndex(str, x);
if (index == -1)
System.out.println("Character not found");
else
System.out.println("Last index is " + index);
}
}
/* This code is contributed by Prerna Saini */
# A Python program to find last
# index of character x in given
# string.
# Returns last index of x if it
# is present. Else returns -1.
def findLastIndex(str, x):
index = -1
for i in range(0, len(str)):
if str[i] == x:
index = i
return index
# Driver program
# String in which char is to be found
str = "geeksforgeeks"
# char whose index is to be found
x = 'e'
index = findLastIndex(str, x)
if index == -1:
print("Character not found")
else:
print('Last index is', index)
# This code is contributed by shrikant13.
// C# program to find last index
// of character x in given string.
using System;
class GFG {
// Returns last index of x if
// it is present Else returns -1.
static int findLastIndex(string str, char x)
{
int index = -1;
for (int i = 0; i < str.Length; i++)
if (str[i] == x)
index = i;
return index;
}
// Driver code
public static void Main()
{
// String in which char is to be found
string str = "geeksforgeeks";
// char whose index is to be found
char x = 'e';
int index = findLastIndex(str, x);
if (index == -1)
Console.WriteLine("Character not found");
else
Console.WriteLine("Last index is " + index);
}
}
/* This code is contributed by vt_m */
<?php
// PHP program to find last index of
// character x in given string.
// Returns last index of
// x if it is present.
// Else returns -1.
function findLastIndex($str, $x)
{
$index = -1;
for ($i = 0; $i < strlen($str); $i++)
if ($str[$i] == $x)
$index = $i;
return $index;
}
// Driver code
// String in which
// char is to be found
$str = "geeksforgeeks";
// char whose index
// is to be found
$x = 'e';
$index = findLastIndex($str, $x);
if ($index == -1)
echo("Character not found");
else
echo("Last index is " . $index);
// This code is contributed by Ajit.
?>
<script>
// javascript program to find last index
// of character x in given string.
// Returns last index of x if
// it is present Else returns -1.
function findLastIndex(str, x)
{
let index = -1;
for (let i = 0; i < str.length; i++)
if (str[i] == x)
index = i;
return index;
}
// Driver code
// String in which char is to be found
let str = "geeksforgeeks";
// char whose index is to be found
let x = 'e';
let index = findLastIndex(str, x);
if (index == -1)
document.write("Character not found");
else
document.write("Last index is " + index);
// This code is contributed by sanjoy_62.
</script>
Time Complexity : O(n)
Auxiliary Space: O(1)
Method 2 (Efficient : Traverse from right): In above method 1, we always traverse complete string. In this method, we can avoid complete traversal in all those cases when x is present. The idea is to traverse from right side and stop as soon as we find character.
Implementation:
CPP
// Simple CPP program to find last index of
// character x in given string.
#include <iostream>
using namespace std;
// Returns last index of x if it is present.
// Else returns -1.
int findLastIndex(string& str, char x)
{
// Traverse from right
for (int i = str.length() - 1; i >= 0; i--)
if (str[i] == x)
return i;
return -1;
}
// Driver code
int main()
{
string str = "geeksforgeeks";
char x = 'e';
int index = findLastIndex(str, x);
if (index == -1)
cout << "Character not found";
else
cout << "Last index is " << index;
return 0;
}
// Java code to find last index
// character x in given string.
import java.io.*;
class GFG {
// Returns last index of x if
// it is present. Else returns -1.
static int findLastIndex(String str, Character x)
{
// Traverse from right
for (int i = str.length() - 1; i >= 0; i--)
if (str.charAt(i) == x)
return i;
return -1;
}
// Driver code
public static void main(String[] args)
{
String str = "geeksforgeeks";
Character x = 'e';
int index = findLastIndex(str, x);
if (index == -1)
System.out.println("Character not found");
else
System.out.println("Last index is " + index);
}
}
// This code is contributed by Prerna Saini
# Simple Python3 program to find last
# index of character x in given string.
# Returns last index of x if it is
# present. Else returns -1.
def findLastIndex(str, x):
# Traverse from right
for i in range(len(str) - 1, -1,-1):
if (str[i] == x):
return i
return -1
# Driver code
str = "geeksforgeeks"
x = 'e'
index = findLastIndex(str, x)
if (index == -1):
print("Character not found")
else:
print("Last index is " ,index)
# This code is contributed by Smitha
// C# code to find last index
// character x in given string.
using System;
class GFG {
// Returns last index of x if
// it is present. Else returns -1.
static int findLastIndex(string str, char x)
{
// Traverse from right
for (int i = str.Length - 1; i >= 0; i--)
if (str[i] == x)
return i;
return -1;
}
// Driver code
public static void Main()
{
string str = "geeksforgeeks";
char x = 'e';
int index = findLastIndex(str, x);
if (index == -1)
Console.WriteLine("Character not found");
else
Console.WriteLine("Last index is " + index);
}
}
// This code is contributed by vt_m
<?php
// Simple PHP program to find last index
// of character x in given string.
// Returns last index of x if it
// is present. Else returns -1.
function findLastIndex($str, $x)
{
// Traverse from right
for ($i = strlen($str) - 1; $i >= 0; $i--)
if ($str[$i] == $x)
return $i;
return -1;
}
// Driver code
$str = "geeksforgeeks";
$x = 'e';
$index = findLastIndex($str, $x);
if ($index == -1)
echo("Character not found");
else
echo("Last index is " . $index);
// This code is contributed by Ajit.
?>
<script>
// Javascript code to find last index character x in given string.
// Returns last index of x if
// it is present. Else returns -1.
function findLastIndex(str, x)
{
// Traverse from right
for (let i = str.length - 1; i >= 0; i--)
if (str[i] == x)
return i;
return -1;
}
let str = "geeksforgeeks";
let x = 'e';
let index = findLastIndex(str, x);
if (index == -1)
document.write("Character not found");
else
document.write("Last index is " + index);
</script>
Time Complexity : O(n)
Auxiliary Space: O(1)
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