Finding the palindrome index ('substr' version).cpp

const auto diffIt = mismatch(begin(S), begin(S) + S.size()/2, rbegin(S)).first; // first iterator
const auto diffIdx = distance(begin(S), diffIt); // 0-based index of the mismatch
const auto toCheck = S.substr(0, diffIdx) + S.substr(diffIdx + 1);
if (equal(begin(toCheck), begin(toCheck) + toCheck.size()/2, rbegin(toCheck))) // is palindrome?
 cout << diffIdx << endl;
else
 cout << S.size() - diffIdx - 1;