CareerCup Facebook Total number of substring palindrome Leetcode 647

Write a function for retrieving the total number of substring palindromes. 
For example the input is 'abba' then the possible palindromes= a, b, b, a, bb, abba 
So the result is 6. 

Updated at 11/11/2013: 

 

After the interview I got know that the O(n^3) solution is not enough to go to the next round. It would have been better to know before starting implementing the solution unnecessarily ...

 

------------------------------------------------------------------------

Similar to leetcode Longest Palindromic Substring Part II in my blog, the code is like:

 

#include <iostream>
#include <map>
#include <algorithm>
#include <limits.h>
#include <assert.h>
#include <string.h>
#include <vector>
using namespace std;
string preprocess(string s) {
  string res = "^#";
  for (int i = 0; i < s.length(); ++i) {
    res += s[i];
    res += '#';
  }
  res += '$';
  return res;
}
int getPalindromeNum(string s) {
  string str = preprocess(s);
  int i, j, len = str.length(), C = 0, R = 0, res = 0, ii;

  vector<int> T(len + 1, 0), P(len + 1, 0);

  for (i = 1; i < len; ++i) {
    ii = 2*C - i;
    P[i] = (R - i) > 0 ? min(P[ii], R-i) : 0;
    //bug1: P[i] = (R - i) > 0 ? P[i] : 0
    while (str[i + P[i] + 1] == str[i - P[i] - 1])
      ++P[i];
    res += (P[i] + 1) / 2;
    //bug2: res += P[i]; 
    if (i + P[i] > R) {
      C = i;
      R = i + P[i];
    }
  }
  return res;
}
int main() {
  //string s = "abcba";
  string s = "aaaaa";
  
  int res = getPalindromeNum(s);
  return 0;
}

-----------------------------------------------------------------------------------------------------------------------------------------------------------

Leetcode collects this problem:

Given a string, your task is to count how many palindromic substrings in this string.

The substrings with different start indexes or end indexes are counted as different substrings even they consist of same characters.

Example 1:

Input: "abc"
Output: 3
Explanation: Three palindromic strings: "a", "b", "c".

 

Example 2:

Input: "aaa"
Output: 6
Explanation: Six palindromic strings: "a", "a", "a", "aa", "aa", "aaa".

 

Note:

1. The input string length won't exceed 1000.

 

Accepted

147,409

Submissions

249,379

-----------------------------------------------------------

Python 

class Solution:
    def pre_process(self, s):
        res = '^#'
        for ch in s:
            res += ch + '#'
        res += '$'
        return res

    def countSubstrings(self, s):
        s1 = self.pre_process(s)
        l, res, c, r = len(s1), 0, 0, 0
        p = [0 for i in range(l)]

        for i in range(1, l-1): #bug1: for i in range(1, l-1)
            ii = c * 2 - i
            # bug2: p[i] = 0 if ii < 0 else min(p[ii], r)
            p[i] = 0 if ii < 0 else min(p[ii], r-i)
            while (s1[i + p[i] + 1] == s1[i - p[i] - 1]):
                p[i] += 1
            if (i + p[i] > r):
                r = i + p[i]
                c = i
            res += (p[i] + 1) >> 1
        return res

s = Solution()
print(s.countSubstrings("aaa"))