# Smallest character in a string having minimum sum of distances between consecutive repetitions

• Last Updated : 27 May, 2022

Given a string S of size N consisting of lowercase alphabets only, the task is to find the smallest character having a minimum sum of distances between its consecutive repetition. If string S consists of distinct characters only, then print “-1”.

Examples:

Output: b;
Explanation:
For all the characters in the given string, the sum of the required distances are as follows:
Indices of ‘a’ = {0, 1, 4, 5}
=> Sum of the distances of its next repetition = abs(0 – 1) + abs(4 – 1) + abs(5 – 4) = 5
Indices of ‘b’ = {2, 3}
=> Sum of the distances of its next repetition = abs(2 – 3) = 1
‘c’, ‘d’ has no repetition
From the above distances the minimum sum of distance obtained is 1, for the character ‘b’.
Therefore, the required answer is ‘b’.

Input: str = “abcdef”
Output: -1
Explanation:
All the characters in the given string are distinct.

Naive approach: The simplest approach is to traverse the given string and for each character, find the sum of the shortest distances individually. Print the smallest character with the minimum shortest distance.

Time Complexity: O(N*26), where N is the length of the given string.
Auxiliary Space: O(N)

Efficient Approach: The idea is to traverse the string once and find the first and last indices for every character as the sum of the difference between the index between the same characters is the difference between the first and the last character. Follow the below steps to solve the problem:

1. Create the arrays last[] and first[] having the length equals 26 initialize both the arrays as -1.
2. Initialize min with some large number.
3. Traverse the string S and update the first occurrence of the current characters to the current index if it equals to -1.
4. Find the last occurrence of each character and store it in the array last[].
5. Traverse the array and update the index having a minimum difference at each corresponding if both the index has non-negative value.
6. If the minimum index is found at index x, and print the character (x + ‘a’).
7. Otherwise, print “-1”.

Below is the implementation of the above approach:

## C++

 `// C++ program for the above approach` `#include ``using` `namespace` `std;` `// Function to find the character``// repeats with minimum distance``char` `minDistChar(string s)``{``    ``int` `n = s.length();` `    ``// Stores the first and last index``    ``int``* first = ``new` `int``;``    ``int``* last = ``new` `int``;` `    ``// Initialize with -1``    ``for` `(``int` `i = 0; i < 26; i++) {``        ``first[i] = -1;``        ``last[i] = -1;``    ``}` `    ``// Get the values of last and``    ``// first occurrence``    ``for` `(``int` `i = 0; i < n; i++) {` `        ``// Update the first index``        ``if` `(first[s[i] - ``'a'``] == -1) {``            ``first[s[i] - ``'a'``] = i;``        ``}` `        ``// Update the last index``        ``last[s[i] - ``'a'``] = i;``    ``}` `    ``// Initialize min``    ``int` `min = INT_MAX;``    ``char` `ans = ``'1'``;` `    ``// Get the minimum``    ``for` `(``int` `i = 0; i < 26; i++) {` `        ``// Values must not be same``        ``if` `(last[i] == first[i])``            ``continue``;` `        ``// Update the minimum distance``        ``if` `(min > last[i] - first[i]) {``            ``min = last[i] - first[i];``            ``ans = i + ``'a'``;``        ``}``    ``}` `    ``// return ans``    ``return` `ans;``}` `// Driver Code``int` `main()``{``    ``string str = ``"geeksforgeeks"``;` `    ``// Function Call``    ``cout << minDistChar(str);` `    ``return` `0;``}`

## Java

 `// Java program for``// the above approach``import` `java.util.*;``class` `GFG{` `// Function to find the character``// repeats with minimum distance``static` `char` `minDistChar(``char` `[]s)``{``int` `n = s.length;` `// Stores the first and last index``int` `[]first = ``new` `int``[``26``];``int` `[]last = ``new` `int``[``26``];` `// Initialize with -1``for` `(``int` `i = ``0``; i < ``26``; i++)``{``    ``first[i] = -``1``;``    ``last[i] = -``1``;``}` `// Get the values of last and``// first occurrence``for` `(``int` `i = ``0``; i < n; i++)``{``    ``// Update the first index``    ``if` `(first[s[i] - ``'a'``] == -``1``)``    ``{``    ``first[s[i] - ``'a'``] = i;``    ``}` `    ``// Update the last index``    ``last[s[i] - ``'a'``] = i;``}` `// Initialize min``int` `min = Integer.MAX_VALUE;``char` `ans = ``'1'``;` `// Get the minimum``for` `(``int` `i = ``0``; i < ``26``; i++)``{``    ``// Values must not be same``    ``if` `(last[i] == first[i])``    ``continue``;` `    ``// Update the minimum distance``    ``if` `(min > last[i] - first[i])``    ``{``    ``min = last[i] - first[i];``    ``ans = (``char``) (i + ``'a'``);``    ``}``}` `// return ans``return` `ans;``}` `// Driver Code``public` `static` `void` `main(String[] args)``{``String str = ``"geeksforgeeks"``;` `// Function Call``System.out.print(minDistChar(str.toCharArray()));``}``}` `// This code is contributed by shikhasingrajput`

## Python3

 `# Python3 program for the above approach``import` `sys` `# Function to find the character``# repeats with minimum distance``def` `minDistChar(s):``    ` `    ``n ``=` `len``(s)``    ` `    ``# Stores the first and last index``    ``first ``=` `[]``    ``last ``=` `[]``    ` `    ``# Initialize with -1``    ``for` `i ``in` `range``(``26``):``        ``first.append(``-``1``)``        ``last.append(``-``1``)``        ` `    ``# Get the values of last and``    ``# first occurrence``    ``for` `i ``in` `range``(n):``        ` `        ``# Update the first index``        ``if` `(first[``ord``(s[i]) ``-` `ord``(``'a'``)] ``=``=` `-``1``):``            ``first[``ord``(s[i]) ``-` `ord``(``'a'``)] ``=` `i``            ` `        ``# Update the last index``        ``last[``ord``(s[i]) ``-` `ord``(``'a'``)] ``=` `i``        ` `    ``# Initialize the min``    ``min` `=` `sys.maxsize``    ``ans ``=` `'1'``    ` `    ``# Get the minimum``    ``for` `i ``in` `range``(``26``):``        ` `        ``# Values must not be same``        ``if` `(last[i] ``=``=` `first[i]):``            ``continue``        ` `        ``# Update the minimum distance``        ``if` `(``min` `> last[i] ``-` `first[i]):``            ``min` `=` `last[i] ``-` `first[i]``            ``ans ``=` `i ``+` `ord``(``'a'``)``            ` `    ``return` `chr``(ans)``        ` `# Driver Code``if` `__name__ ``=``=` `"__main__"``:``    ` `    ``str` `=` `"geeksforgeeks"` `    ``# Function call``    ``print``(minDistChar(``str``))` `# This code is contributed by dadi madhav`

## C#

 `// C# program for the above approach``using` `System;``using` `System.Collections.Generic; ` `class` `GFG{``  ` `// Function to find the character``// repeats with minimum distance``static` `char` `minDistChar(``char` `[]s)``{``    ``int` `n = s.Length;` `    ``// Stores the first and last index``    ``int` `[]first = ``new` `int``;``    ``int` `[]last = ``new` `int``;` `    ``// Initialize with -1``    ``for``(``int` `i = 0; i < 26; i++)``    ``{``        ``first[i] = -1;``        ``last[i] = -1;``    ``}` `    ``// Get the values of last and``    ``// first occurrence``    ``for``(``int` `i = 0; i < n; i++)``    ``{` `        ``// Update the first index``        ``if` `(first[s[i] - ``'a'``] == -1)``        ``{``              ``first[s[i] - ``'a'``] = i;``        ``}` `        ``// Update the last index``        ``last[s[i] - ``'a'``] = i;``    ``}` `    ``// Initialize min``    ``int` `min = ``int``.MaxValue;``    ``char` `ans = ``'1'``;` `    ``// Get the minimum``    ``for``(``int` `i = 0; i < 26; i++)``    ``{``        ``// Values must not be same``        ``if` `(last[i] == first[i])``            ``continue``;` `        ``// Update the minimum distance``        ``if` `(min > last[i] - first[i])``        ``{``            ``min = last[i] - first[i];``            ``ans = (``char``)(i + ``'a'``);``        ``}``    ``}``  ` `    ``// return ans``    ``return` `ans;``}``  ` `// Driver Code``public` `static` `void` `Main(``string``[] args)``{ ``    ``String str = ``"geeksforgeeks"``;`` ` `    ``// Function call``    ``Console.Write(minDistChar(str.ToCharArray()));``}``}` `// This code is contributed by rutvik_56`

## Javascript

 ``

Output:

`g`

Time Complexity: O(N)
Auxiliary Space: O(N)

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