Data Structure
Networking
RDBMS
Operating System
Java
MS Excel
iOS
HTML
CSS
Android
Python
C Programming
C++
C#
MongoDB
MySQL
Javascript
PHP
Physics
Chemistry
Biology
Mathematics
English
Economics
Psychology
Social Studies
Fashion Studies
Legal Studies
- Selected Reading
- UPSC IAS Exams Notes
- Developer's Best Practices
- Questions and Answers
- Effective Resume Writing
- HR Interview Questions
- Computer Glossary
- Who is Who
Find the Closest Palindrome in C++
Suppose we have a number n, we have to get the closest number that is palindrome. So the palindrome could be less than or greater than the number whose absolute difference is smaller. So if the number is like 145, then the result will be 141.
To solve this, we will follow these steps −
- sn := size of n
- if sn is same as 1, then −
- decrease n[0] by 1 and return a string of 1s of size n[0]
- half_sn := (sn + 1) / 2
- half_val := stol(substring of n from index 0 to half_sn
- Define an array candidates = {10^(sn) – 1, 10^(sn - 1) - 1, 10^(sn - 1) + 1, 10^(sn)+1
- Define an array fmdc = { half_val, half_val - 1, half_val + 1 }
- for each value c in fmds
- rev := convert c to string
- if sn mod 2 is non-zero, then −
- delete last element from rev
- reverse the array rev
- insert c at the end of candidates
- sort the array candidates
- val := n as integer
- for each candidate in candidates −
- if candidate is same as val, then −
- Ignore following part, skip to the next iteration
- diff := abs|candidate – val|
- if diff < min_diff, then −
- min_diff := diff
- ans := convert candidate to string
- if candidate is same as val, then −
- return ans
Let us see the following implementation to get better understanding −
Example
#include <bits/stdc++.h>
using namespace std;
class Solution {
public:
string nearestPalindromic(string n) {
int sn = n.size();
if(sn == 1){
return string(1, --n[0]);
}
int half_sn = (sn+1)/2;
long half_val = stol(n.substr(0, half_sn));
vector<long> candidates = {pow(10, sn)-1, pow(10, sn-1)-1, pow(10, sn-1)+1, pow(10, sn)+1};
vector <long> fmdc = {half_val, half_val-1,half_val+1};
for(long c:fmdc){
string rev = to_string(c);
if(sn%2)rev.pop_back();
reverse(rev.begin(),rev.end());
candidates.push_back(stol(to_string(c) + rev));
}
sort(candidates.begin(), candidates.end());
string ans;
long val = stol(n), min_diff = INT_MAX;
for(long candidate : candidates){
if(candidate == val)continue;
long diff = labs(candidate - val);
if(diff < min_diff){
min_diff = diff;
ans = to_string(candidate);
}
}
return ans;
}
};
main(){
Solution ob;
cout << (ob.nearestPalindromic("145"));
}Input
“145”
Output
141
Updated on: 01-Jun-2020
154 Views
Advertisements