Problem link -http://codeforces.com/contest/486/problem/C
Logic:
Check the number of characters that need to be changed inorder to make the given string palindrome.let the count be stored in variable ‘diff’.
It is optimal and sufficient to make changes to characters in any one of half of the string.
Lets choose the first half.
Case 1:
p is in first half of the string.
ans=diff+minimum number of steps required to move to all character positions that needs to be changed from position p
Case 2:
p is in 2nd half of the string.
Now reverse the string and make p=n-p+1
ans=diff+minimum number of steps required to move to all character positions that needs to be changed from position p
Thats all !
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| #include <vector> | |
| #include <list> | |
| #include <map> | |
| #include <set> | |
| #include <deque> | |
| #include <queue> | |
| #include <stack> | |
| #include <bitset> | |
| #include <algorithm> | |
| #include <functional> | |
| #include <numeric> | |
| #include <utility> | |
| #include <sstream> | |
| #include <iostream> | |
| #include <iomanip> | |
| #include <cstdio> | |
| #include <cmath> | |
| #include <cstdlib> | |
| #include <ctime> | |
| #include <cstring> | |
| #include <climits> | |
| #include <stdlib.h> | |
| #include <stdio.h> | |
| using namespace std; | |
| #define REP(i,n) for(int i=0; i<n; i++) | |
| #define FOR(i,st,end) for(int i=st;i<end;i++) | |
| #define db(x) cout << (#x) << " = " << x << endl; | |
| #define mp make_pair | |
| #define pb push_back | |
| #define MAX 10000005 | |
| typedef long long int ll; | |
| int main(){ | |
| int n,p; | |
| string str; | |
| scanf("%d%d",&n,&p); | |
| p--; | |
| cin>>str; | |
| int firstr; | |
| firstr=n/2-1; | |
| int diff=0; | |
| //maxi - index of the rightmost character that needs to be changed in the first half of the string | |
| //mini - index of the leftmost character that needs to be changed in the first half of the string | |
| int mini=99999,maxi=-1; | |
| if(p>firstr){ | |
| reverse(str.begin(),str.end()); | |
| p=n-1-p; | |
| } | |
| REP(i,firstr+1){ | |
| if(str[i]!=str[n-1-i]){ | |
| diff+=min((abs(str[i]-str[n-1-i])),abs(('z'-max(str[i],str[n-1-i]))+min(str[i],str[n-1-i])-'a'+1)); | |
| mini=min(mini,i); | |
| maxi=max(maxi,i); | |
| } | |
| } | |
| if(maxi>p&&mini<p){ | |
| if(abs(p-maxi)<abs(p-mini)){ | |
| diff+=abs(p-maxi)*2; | |
| diff+=abs(p-mini); | |
| } | |
| else{ | |
| diff+=abs(p-mini)*2; | |
| diff+=abs(p-maxi); | |
| } | |
| } | |
| else if(maxi>p) | |
| diff+=abs(p-maxi); | |
| else if(mini<p) | |
| diff+=abs(p-mini); | |
| cout<<diff; | |
| } |
coding hangover 