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Java-based LeetCode algorithm problem solutions, regularly updated
package g1301_1400.s1316_distinct_echo_substrings;
// #Hard #String #Dynamic_Programming #Sliding_Window #Trie #Hash_Function #Rolling_Hash
// #2022_03_19_Time_165_ms_(93.15%)_Space_65.3_MB_(55.48%)
import java.util.HashSet;
import java.util.Set;
/**
* 1316 - Distinct Echo Substrings\.
*
* Hard
*
* Return the number of **distinct** non-empty substrings of `text` that can be written as the concatenation of some string with itself (i.e. it can be written as `a + a` where `a` is some string).
*
* **Example 1:**
*
* **Input:** text = "abcabcabc"
*
* **Output:** 3
*
* **Explanation:** The 3 substrings are "abcabc", "bcabca" and "cabcab".
*
* **Example 2:**
*
* **Input:** text = "leetcodeleetcode"
*
* **Output:** 2
*
* **Explanation:** The 2 substrings are "ee" and "leetcodeleetcode".
*
* **Constraints:**
*
* * `1 <= text.length <= 2000`
* * `text` has only lowercase English letters.
**/
public class Solution {
private static final int PRIME = 101;
private static final int MOD = 1_000_000_007;
public int distinctEchoSubstrings(String text) {
int n = text.length();
int[][] dp = new int[n][n];
for (int i = 0; i < n; i++) {
long hash = 0;
for (int j = i; j < n; j++) {
hash = hash * PRIME + (text.charAt(j) - 'a' + 1);
hash %= MOD;
dp[i][j] = (int) hash;
}
}
Set set = new HashSet<>();
int res = 0;
for (int i = 0; i < n - 1; i++) {
for (int j = i; 2 * j - i + 1 < n; j++) {
if (dp[i][j] == dp[j + 1][2 * j - i + 1] && set.add(dp[i][j])) {
res++;
}
}
}
return res;
}
}
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