LeetCode-in-Java
1513. Number of Substrings With Only 1s
Medium
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 109 + 7.
Example 1:
Input: s = “0110111”
Output: 9
Explanation: There are 9 substring in total with only 1’s characters. “1” -> 5 times. “11” -> 3 times. “111” -> 1 time.
Example 2:
Input: s = “101”
Output: 2
Explanation: Substring “1” is shown 2 times in s.
Example 3:
Input: s = “111111”
Output: 21
Explanation: Each substring contains only 1’s characters.
Constraints:
1 <= s.length <= 105s[i]is either'0'or'1'.
Solution
public class Solution {
public int numSub(String s) {
long count = 0;
long res = 0;
for (char ch : s.toCharArray()) {
if (ch == '0') {
res += count * (count + 1) / 2;
count = 0;
} else {
count++;
}
}
res += count * (count + 1) / 2;
return (int) (res % 1000000007);
}
}