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// 1930. Unique Length-3 Palindromic Subsequences
#include "leetcode.h"
/*
* given a string 's', return the number of unique palindromes of length three
* that that are a subsequence of 's'. note that even if there are multiple ways
* to obtain the same subsequence, it is still only counted once. a palindrome
* is a string that reads the same forwards and backwards. a subsequence of a
* string is a new string generated from the original string with some
* characters (can be none) deleted without changing the relative order of thhe
* remaining characters. for example: "ace" is a subsequence of "abcde"
*/
int countPalindromicSubsequence(char *s) {
int n = strlen(s), ans = 0;
bool *alpha = calloc(26, sizeof(bool));
bool *tmp;
for (int i = 0; i < n; i++) {
if (alpha[s[i] - 'a'])
continue;
alpha[s[i] - 'a'] = 1;
char c = s[i];
for (int j = n - 1; j > i + 1; j--) {
if (s[j] == s[i]) {
tmp = calloc(26, sizeof(char));
for (int k = i + 1; k < j; k++) {
if (!tmp[s[k] - 'a']) {
tmp[s[k] - 'a'] = 1;
ans++;
}
}
break;
}
}
}
return ans;
}
int main() {
char s1[] = {"aabca"}, s2[] = {"adc"}, s3[] = {"bbcbaba"};
printf("%d\n", countPalindromicSubsequence(s1)); // expect: 3
printf("%d\n", countPalindromicSubsequence(s2)); // expect: 0
printf("%d\n", countPalindromicSubsequence(s3)); // expect: 4
}
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