Index of character depending on frequency count in string
Last Updated :
29 Dec, 2022
Given a string str containing only lowercase characters, the task is to answer Q queries of the following type:
- 1 C X: Find the largest i such that str[0...i] has exactly X occurrence of the character C.
- 2 C X: Find the smallest i such that str[0...i] has exactly X occurrence of the character C.
Example:
Input: str = "geeksforgeeks", query[] = {{1, 'e', 2}, {2, 'k', 2}}
Output:
8
11
Query 1: "geeksforg" is the largest substring starting at str[0] with 'e' appearing exactly twice and the index of the last character is 8.
Query 2: "geeksforgeek" is the smallest substring starting at str[0] with 'k' appearing exactly twice and the index of the last character is 11.
Input: str = "abcdabcd", query[] = {{1, 'a', 1}, {2, 'a', 2}}
Output:
3
4
Approach: Create two 2-dimensional arrays L[][] and F[][] such that L[i][j] stores the largest i such that the ith character appears exactly jth times in str[0...i] and F[i][j] stores the smallest i such that the ith character appears exactly jth times in str[0...i]. In order to do so, traverse the whole string and maintain a frequency array so that for each iteration/character, its count is updated and then start another loop from 0 to 26 (each letter a-z). In the inner loop, if the iterator is equal to character value then update L[][] and F[][] array with the current index position using outer loop iterator otherwise just increment the L[][] array value for other characters by 1 as only index has been incremented and the character has not occurred. Now, type 1 query can be answered as L[given character][Frequency count] and type 2 query as F[given character][Frequency count].
Below is the implementation of the above approach.
C++
// C++ implementation of the approach
#include <bits/stdc++.h>
using namespace std;
const int MAX = 26;
// Function to perform the queries
void performQueries(string str, int q, int type[],
char ch[], int freq[])
{
int n = str.length();
// L[i][j] stores the largest i
// such that ith character appears
// exactly jth times in str[0...i]
int L[MAX][n];
// F[i][j] stores the smallest i
// such that ith character appears
// exactly jth times in str[0...i]
int F[MAX][n];
// To store the frequency of each
// of the character of str
int cnt[MAX] = { 0 };
for (int i = 0; i < n; i++) {
// Current character of str
int k = str[i] - 'a';
// Update its frequency
cnt[k]++;
// For every lowercase character
// of the English alphabet
for (int j = 0; j < MAX; j++) {
// If it is equal to the character
// under consideration then update
// L[][] and R[][] as it is cnt[j]th
// occurrence of character k
if (k == j) {
L[j][cnt[j]] = i;
F[j][cnt[j]] = i;
}
// Only update L[][] as k has not
// been occurred so only index
// has to be incremented
else
L[j][cnt[j]] = L[j][cnt[j]] + 1;
}
}
// Perform the queries
for (int i = 0; i < q; i++) {
// Type 1 query
if (type[i] == 1) {
cout << L[ch[i] - 'a'][freq[i]];
}
// Type 2 query
else {
cout << F[ch[i] - 'a'][freq[i]];
}
cout << "\n";
}
}
// Driver code
int main()
{
string str = "geeksforgeeks";
// Queries
int type[] = { 1, 2 };
char ch[] = { 'e', 'k' };
int freq[] = { 2, 2 };
int q = sizeof(type) / sizeof(int);
// Perform the queries
performQueries(str, q, type, ch, freq);
return 0;
}
// Java implementation of the approach
class GFG
{
static int MAX = 26;
// Function to perform the queries
static void performQueries(String str, int q, int type[],
char ch[], int freq[])
{
int n = str.length();
// L[i][j] stores the largest i
// such that ith character appears
// exactly jth times in str[0...i]
int [][]L = new int[MAX][n];
// F[i][j] stores the smallest i
// such that ith character appears
// exactly jth times in str[0...i]
int [][]F = new int[MAX][n];
// To store the frequency of each
// of the character of str
int []cnt = new int[MAX];
for (int i = 0; i < n; i++)
{
// Current character of str
int k = str.charAt(i) - 'a';
// Update its frequency
cnt[k]++;
// For every lowercase character
// of the English alphabet
for (int j = 0; j < MAX; j++)
{
// If it is equal to the character
// under consideration then update
// L[][] and R[][] as it is cnt[j]th
// occurrence of character k
if (k == j)
{
L[j][cnt[j]] = i;
F[j][cnt[j]] = i;
}
// Only update L[][] as k has not
// been occurred so only index
// has to be incremented
else
L[j][cnt[j]] = L[j][cnt[j]] + 1;
}
}
// Perform the queries
for (int i = 0; i < q; i++)
{
// Type 1 query
if (type[i] == 1)
{
System.out.print(L[ch[i] - 'a'][freq[i]]);
}
// Type 2 query
else
{
System.out.print(F[ch[i] - 'a'][freq[i]]);
}
System.out.print("\n");
}
}
// Driver code
public static void main(String []args)
{
String str = "geeksforgeeks";
// Queries
int type[] = { 1, 2 };
char ch[] = { 'e', 'k' };
int freq[] = { 2, 2 };
int q = type.length;
// Perform the queries
performQueries(str, q, type, ch, freq);
}
}
// This code is contributed by Rajput-Ji
# Python3 implementation of the approach
import numpy as np
MAX = 26;
# Function to perform the queries
def performQueries(string , q, type_arr, ch, freq) :
n = len(string);
# L[i][j] stores the largest i
# such that ith character appears
# exactly jth times in str[0...i]
L = np.zeros((MAX, n));
# F[i][j] stores the smallest i
# such that ith character appears
# exactly jth times in str[0...i]
F = np.zeros((MAX, n));
# To store the frequency of each
# of the character of str
cnt = [ 0 ] * MAX;
for i in range(n) :
# Current character of str
k = ord(string[i]) - ord('a');
# Update its frequency
cnt[k] += 1;
# For every lowercase character
# of the English alphabet
for j in range(MAX) :
# If it is equal to the character
# under consideration then update
# L[][] and R[][] as it is cnt[j]th
# occurrence of character k
if (k == j) :
L[j][cnt[j]] = i;
F[j][cnt[j]] = i;
# Only update L[][] as k has not
# been occurred so only index
# has to be incremented
else :
L[j][cnt[j]] = L[j][cnt[j]] + 1;
# Perform the queries
for i in range(q) :
# Type 1 query
if (type_arr[i] == 1) :
print(L[ord(ch[i]) -
ord('a')][freq[i]], end = "");
# Type 2 query
else :
print(F[ord(ch[i]) -
ord('a')][freq[i]], end = "");
print()
# Driver code
if __name__ == "__main__" :
string = "geeksforgeeks";
# Queries
type_arr = [ 1, 2 ];
ch = [ 'e', 'k' ];
freq = [ 2, 2 ];
q = len(type_arr);
# Perform the queries
performQueries(string, q, type_arr, ch, freq);
# This code is contributed by AnkitRai01
// C# implementation of the approach
using System;
class GFG
{
static int MAX = 26;
// Function to perform the queries
static void performQueries(String str, int q, int []type,
char []ch, int []freq)
{
int n = str.Length;
// L[i,j] stores the largest i
// such that ith character appears
// exactly jth times in str[0...i]
int [,]L = new int[MAX, n];
// F[i,j] stores the smallest i
// such that ith character appears
// exactly jth times in str[0...i]
int [,]F = new int[MAX, n];
// To store the frequency of each
// of the character of str
int []cnt = new int[MAX];
for (int i = 0; i < n; i++)
{
// Current character of str
int k = str[i] - 'a';
// Update its frequency
cnt[k]++;
// For every lowercase character
// of the English alphabet
for (int j = 0; j < MAX; j++)
{
// If it is equal to the character
// under consideration then update
// L[,] and R[,] as it is cnt[j]th
// occurrence of character k
if (k == j)
{
L[j, cnt[j]] = i;
F[j, cnt[j]] = i;
}
// Only update L[,] as k has not
// been occurred so only index
// has to be incremented
else
L[j, cnt[j]] = L[j, cnt[j]] + 1;
}
}
// Perform the queries
for (int i = 0; i < q; i++)
{
// Type 1 query
if (type[i] == 1)
{
Console.Write(L[ch[i] - 'a', freq[i]]);
}
// Type 2 query
else
{
Console.Write(F[ch[i] - 'a', freq[i]]);
}
Console.Write("\n");
}
}
// Driver code
public static void Main(String []args)
{
String str = "geeksforgeeks";
// Queries
int []type = { 1, 2 };
char []ch = { 'e', 'k' };
int []freq = { 2, 2 };
int q = type.Length;
// Perform the queries
performQueries(str, q, type, ch, freq);
}
}
// This code is contributed by 29AjayKumar
<script>
// JavaScript implementation of the approach
let MAX = 26;
// Function to perform the queries
function performQueries(str, q, type, ch, freq)
{
let n = str.length;
// L[i][j] stores the largest i
// such that ith character appears
// exactly jth times in str[0...i]
let L = new Array(MAX);
// F[i][j] stores the smallest i
// such that ith character appears
// exactly jth times in str[0...i]
let F = new Array(MAX);
// To store the frequency of each
// of the character of str
let cnt = new Array(MAX);
for (let i = 0; i < MAX; i++)
{
L[i] = new Array(n);
F[i] = new Array(n);
cnt[i] = 0;
for (let j = 0; j < n; j++)
{
L[i][j] = 0;
F[i][j] = 0;
}
}
for (let i = 0; i < n; i++)
{
// Current character of str
let k = str[i].charCodeAt() - 'a'.charCodeAt();
// Update its frequency
cnt[k]++;
// For every lowercase character
// of the English alphabet
for (let j = 0; j < MAX; j++)
{
// If it is equal to the character
// under consideration then update
// L[][] and R[][] as it is cnt[j]th
// occurrence of character k
if (k == j)
{
L[j][cnt[j]] = i;
F[j][cnt[j]] = i;
}
// Only update L[][] as k has not
// been occurred so only index
// has to be incremented
else
L[j][cnt[j]] = L[j][cnt[j]] + 1;
}
}
// Perform the queries
for (let i = 0; i < q; i++)
{
// Type 1 query
if (type[i] == 1)
{
document.write(L[ch[i].charCodeAt() -
'a'.charCodeAt()][freq[i]]);
}
// Type 2 query
else
{
document.write(F[ch[i].charCodeAt() -
'a'.charCodeAt()][freq[i]]);
}
document.write("</br>");
}
}
let str = "geeksforgeeks";
// Queries
let type = [ 1, 2 ];
let ch = [ 'e', 'k' ];
let freq = [ 2, 2 ];
let q = type.length;
// Perform the queries
performQueries(str, q, type, ch, freq);
</script>
Time Complexity: O(n)
Auxiliary Space: O(26 * n)
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