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Sum of all palindromic numbers lying in the range [L, R] for Q queries
  • Last Updated : 15 Jun, 2020

Given Q queries in the form of 2D array arr[][] whose every row consists of two numbers L and R which denotes the range [L, R], the task is to find the sum of all Palindrome Numbers lying in range [L, R].

Input: Q = 2, arr[][] = { {10, 13}, {12, 21} }
Output:
11
0
Explanation:
From 10 to 13 only 11 is the palindrome number
From 12 to 21 there is no palindromic number

Input: Q = 4, arr[][] = { { 10, 10 }, { 258, 785 }, {45, 245 }, { 1, 1000} }
Output:
0
27024
2955
50040

Approach:
The idea is to use the prefix sum array. The sum of all palindromic number till that particular index is precomputed and stored in an array pref[] so that every query can be answered in O(1) time.

  1. Initialise the prefix array pref[].
  2. Iterate from 1 to N and check if the number is palindromic or not:
    • If the number is palindromic then, the current index of pref[] will store the sum of the number and the number at previous index of pref[].
    • Else the current index of pref[] is same as the value at previous index of pref[].
  3. For Q queries the sum of all palindromic numbers for range [L, R] can be found as follows:
    sum = pref[R] - pref[L - 1]
    

Below is the implementation of the above approach

C++



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// C++ program to find the sum
// of all palindrome numbers
// in the given range
#include <bits/stdc++.h>
using namespace std;
  
// pref[] array to precompute
// the sum of all palindromic
// number
long long pref[100001];
  
// Function that return number
// num if num is palindromic
// else return 0
int checkPalindrome(int num)
{
  
    // Convert num to string
    string str = to_string(num);
  
    int l = 0, r = str.length() - 1;
  
    while (l < r) {
        if (str[l] != str[r]) {
            return 0;
        }
        l++;
        r--;
    }
    return num;
}
  
// Function to precompute the
// sum of all palindrome numbers
// upto 100000
void preCompute()
{
    for (int i = 1; i <= 100000; ++i) {
  
        // checkPalindrome()
        // return the number i
        // if i is palindromic
        // else return 0
        pref[i] = pref[i - 1]
                  + checkPalindrome(i);
    }
}
  
// Function to print the sum
// for each query
void printSum(int L, int R)
{
    cout << pref[R] - pref[L - 1]
         << endl;
}
  
// Function to print sum of all
// palindromic numbers between
// [L, R]
void printSumPalindromic(int arr[][2],
                         int Q)
{
  
    // Function that pre computes
    // the sum of all palindromic
    // numbers
    preCompute();
  
    // Iterate over all Queries
    // to print the sum
    for (int i = 0; i < Q; i++) {
        printSum(arr[i][0], arr[i][1]);
    }
}
  
// Driver code
int main()
{
    // Queries
    int Q = 2;
    int arr[][2] = { { 10, 13 },
                     { 12, 21 } };
  
    // Function that print the
    // the sum of all palindromic
    // number in Range [L, R]
    printSumPalindromic(arr, Q);
    return 0;
}

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Java

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// Java program to find the sum
// of all palindrome numbers
// in the given range
import java.util.*;
  
class GFG{
   
// pref[] array to precompute
// the sum of all palindromic
// number
static int []pref = new int[100001];
   
// Function that return number
// num if num is palindromic
// else return 0
static int checkPalindrome(int num)
{
   
    // Convert num to String
    String str = String.valueOf(num);
   
    int l = 0, r = str.length() - 1;
   
    while (l < r) {
        if (str.charAt(l) != str.charAt(r)) {
            return 0;
        }
        l++;
        r--;
    }
    return num;
}
   
// Function to precompute the
// sum of all palindrome numbers
// upto 100000
static void preCompute()
{
    for (int i = 1; i <= 100000; ++i) {
   
        // checkPalindrome()
        // return the number i
        // if i is palindromic
        // else return 0
        pref[i] = pref[i - 1]
                  + checkPalindrome(i);
    }
}
   
// Function to print the sum
// for each query
static void printSum(int L, int R)
{
    System.out.print(pref[R] - pref[L - 1]
         +"\n");
}
   
// Function to print sum of all
// palindromic numbers between
// [L, R]
static void printSumPalindromic(int arr[][],
                         int Q)
{
   
    // Function that pre computes
    // the sum of all palindromic
    // numbers
    preCompute();
   
    // Iterate over all Queries
    // to print the sum
    for (int i = 0; i < Q; i++) {
        printSum(arr[i][0], arr[i][1]);
    }
}
   
// Driver code
public static void main(String[] args)
{
    // Queries
    int Q = 2;
    int arr[][] = { { 10, 13 },
                     { 12, 21 } };
   
    // Function that print the
    // the sum of all palindromic
    // number in Range [L, R]
    printSumPalindromic(arr, Q);
}
}
  
// This code is contributed by 29AjayKumar

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Python3

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# Python3 program to find the sum
# of all palindrome numbers
# in the given range
  
# pref[] array to precompute
# the sum of all palindromic
# number
pref=[0]*100001
  
# Function that return number
# num if num is palindromic
# else return 0
def checkPalindrome(num):
      
    # Convert num to string
    strr = str(num)
    l = 0
    r = len(strr)- 1
    while (l < r):
        if (strr[l] != strr[r]):
            return 0
              
        l+=1
        r-=1
      
    return num
  
  
# Function to precompute the
# sum of all palindrome numbers
# upto 100000
def preCompute():
    for i in range(1,100001):
        # checkPalindrome()
        # return the number i
        # if i is palindromic
        # else return 0
        pref[i] = pref[i - 1]+ checkPalindrome(i)
      
  
  
# Function to print the sum
# for each query
def printSum(L, R):
    print(pref[R] - pref[L - 1])
  
  
# Function to prsum of all
# palindromic numbers between
# [L, R]
def printSumPalindromic(arr,Q):
      
    # Function that pre computes
    # the sum of all palindromic
    # numbers
    preCompute()
      
    # Iterate over all Queries
    # to print the sum
    for i in range(Q):
        printSum(arr[i][0], arr[i][1])
      
  
  
# Driver code
  
# Queries
Q = 2
arr= [[10, 13 ],[ 12, 21 ]]
  
# Function that print the
# the sum of all palindromic
# number in Range [L, R]
printSumPalindromic(arr, Q)
  
# This code is contributed by shivanisinghss2110

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C#

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// C# program to find the sum
// of all palindrome numbers
// in the given range
using System;
  
class GFG{
    
// pref[] array to precompute
// the sum of all palindromic
// number
static int []pref = new int[100001];
    
// Function that return number
// num if num is palindromic
// else return 0
static int checkPalindrome(int num)
{
    
    // Convert num to String
    String str = String.Join("",num);
    
    int l = 0, r = str.Length - 1;
    
    while (l < r) {
        if (str[l] != str[r]) {
            return 0;
        }
        l++;
        r--;
    }
    return num;
}
    
// Function to precompute the
// sum of all palindrome numbers
// upto 100000
static void preCompute()
{
    for (int i = 1; i <= 100000; ++i) {
    
        // checkPalindrome()
        // return the number i
        // if i is palindromic
        // else return 0
        pref[i] = pref[i - 1]
                  + checkPalindrome(i);
    }
}
    
// Function to print the sum
// for each query
static void printSum(int L, int R)
{
    Console.Write(pref[R] - pref[L - 1]
         +"\n");
}
    
// Function to print sum of all
// palindromic numbers between
// [L, R]
static void printSumPalindromic(int [,]arr,
                         int Q)
{
    
    // Function that pre computes
    // the sum of all palindromic
    // numbers
    preCompute();
    
    // Iterate over all Queries
    // to print the sum
    for (int i = 0; i < Q; i++) {
        printSum(arr[i,0], arr[i,1]);
    }
}
    
// Driver code
public static void Main(String[] args)
{
    // Queries
    int Q = 2;
    int [,]arr = { { 10, 13 },
                     { 12, 21 } };
    
    // Function that print the
    // the sum of all palindromic
    // number in Range [L, R]
    printSumPalindromic(arr, Q);
}
}
  
// This code is contributed by PrinciRaj1992

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Output:

11
0

Time Complexity: O(N)

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