1147 - Longest Chunked Palindrome Decomposition (Hard)

Problem Link

https://leetcode.com/problems/longest-chunked-palindrome-decomposition/

Problem Statement

You are given a string text. You should split it to k substrings (subtext1, subtext2, ..., subtextk) such that:

• subtexti is a non-empty string.
• The concatenation of all the substrings is equal to text (i.e., subtext1 + subtext2 + ... + subtextk == text).
• subtexti == subtextk - i + 1 for all valid values of i (i.e., 1 <= i <= k).

Return the largest possible value of k.

Example 1:

Input: text = "ghiabcdefhelloadamhelloabcdefghi"
Output: 7
Explanation: We can split the string on "(ghi)(abcdef)(hello)(adam)(hello)(abcdef)(ghi)".

Example 2:

Input: text = "merchant"
Output: 1
Explanation: We can split the string on "(merchant)".

Example 3:

Input: text = "antaprezatepzapreanta"
Output: 11
Explanation: We can split the string on "(a)(nt)(a)(pre)(za)(tpe)(za)(pre)(a)(nt)(a)".

Constraints:

• 1 <= text.length <= 1000
• text consists only of lowercase English characters.

Approach 1: Greedy

Build the subtext from the left $l = l + text[i]$ and from the right $r = text[n - 1 - i] + r$. If at a point they are same, then increase the answer by $1$ and reset both $l$ and $r$.

Written by @wingkwong

class Solution {
public:
    int longestDecomposition(string text) {
        int n = text.size(), ans = 0;
        string l, r;
        for (int i = 0; i < n; i++) {
            // build subtect from the left
            l = l + text[i];
            // build subtect from the right
            r = text[n - 1 - i] + r;
            // if they are same, 
            if (l == r) {
                // then increase answer by 1
                ans += 1;
                // reset l & r
                l = r = "";
            }
        }
        return ans;
    }
};