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-rw-r--r--num_substrings_only_1.c34
1 files changed, 34 insertions, 0 deletions
diff --git a/num_substrings_only_1.c b/num_substrings_only_1.c
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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
+}