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// 1759. Count Number of Homogenous Substrings
#include "leetcode.h"
/*
* given a string 's', return the number of homogenous substrings of 's'. since
* thhe answer may be very large, return it modulo 10^9+7. a string is
* homogenous if all the characters of the string are the same. a substring is a
* continuous sequence of chharacters within a string.
*/
int countHomogenous(char *s) {
int ans = 0, mod = 1e9 + 7, n = strlen(s), cnt = 1;
for (int i = 1; i < n; i++) {
if (s[i] == s[i - 1])
cnt++;
else {
long val = (1 + cnt) * cnt / 2;
ans = (ans + val % mod) % mod;
cnt = 1;
}
}
long long val = (long long)(1 + cnt) * cnt / 2;
ans = (ans + val % mod) % mod;
return ans;
}
int main() {
char s1[] = {"abbcccaa"}, s2[] = {"xy"}, s3[] = {"zzzzz"};
printf("%d\n", countHomogenous(s1)); // expect: 13
printf("%d\n", countHomogenous(s2)); // expect: 2
printf("%d\n", countHomogenous(s3)); // expect: 15
}
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