diff --git a/Cpp/LongestPalindromeSubstring.cpp b/Cpp/LongestPalindromeSubstring.cpp new file mode 100644 index 0000000..a987812 --- /dev/null +++ b/Cpp/LongestPalindromeSubstring.cpp @@ -0,0 +1,59 @@ +// A O(n^2) time and O(1) space program to +// find the longest palindromic substring +// easy to understand as compared to previous version. +#include +using namespace std; + +// A utility function to print +// a substring str[low..high] +// This function prints the +// longest palindrome substring (LPS) +// of str[]. It also returns the +// length of the longest palindrome +int longestPalSubstr(string str) +{ + int n = str.size(); // calculating size of string + if (n < 2) + return n; // if string is empty then size will be 0. + // if n==1 then, answer will be 1(single + // character will always palindrome) + + int maxLength = 1, start = 0; + int low, high; + for (int i = 0; i < n; i++) { + low = i - 1; + high = i + 1; + while (high < n + && str[high] == str[i]) // increment 'high' + high++; + + while (low >= 0 + && str[low] == str[i]) // decrement 'low' + low--; + + while (low >= 0 && high < n + && str[low] == str[high]) { + low--; + high++; + } + + int length = high - low - 1; + if (maxLength < length) { + maxLength = length; + start = low + 1; + } + } + + cout << "Longest palindrome substring is: "; + cout << str.substr(start, maxLength); + return maxLength; +} + +// Driver program to test above functions +int main() +{ + string str = "forgeeksskeegfor"; + cout << "\nLength is: " << longestPalSubstr(str) + << endl; + return 0; +}