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// 1513. Number of Substrings With Only 1s
#include "leetcode.h"
/*
* given a binary string 's', return the number of substrings with all
* characters 1's since the answer may be too large, return it modulo 1e9+7.
*/
int numSub(char *s) {
int n = strlen(s), mod = 1e9 + 7, ans = 0, one_cnt = 0;
for (int i = 0; i < n; i++) {
if (s[i] == '1')
one_cnt++;
else {
if (one_cnt) {
long long val = (long long)(one_cnt + 1) * one_cnt / 2;
ans = (ans + val % mod) % mod;
}
one_cnt = 0;
}
}
if (one_cnt) {
long long val = (long long)(one_cnt + 1) * one_cnt / 2;
ans = (ans + val % mod) % mod;
}
return ans;
}
int main() {
char *s1 = "0110111", *s2 = "101", *s3 = "11111";
printf("%d\n", numSub(s1)); // expect: 9
printf("%d\n", numSub(s2)); // expect: 2
printf("%d\n", numSub(s3)); // expect: 21
}
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