LeetCode 1513: Number of Substrings With Only 1s Solution
Master LeetCode problem 1513 (Number of Substrings With Only 1s), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.
Problem Explanation
Explanation
To solve this problem, we can iterate through the binary string and count the continuous sequences of 1s. For every sequence of length n, the number of substrings that can be formed using that sequence is (n * (n + 1)) / 2. We calculate this for each sequence of 1s and sum up the results to get the total number of substrings with only 1s.
Solution Code
class Solution {
public int numSub(String s) {
int count = 0;
int result = 0;
int mod = 1000000007;
for (char c : s.toCharArray()) {
if (c == '1') {
count++;
} else {
result = (result + (count * (count + 1) / 2) % mod) % mod;
count = 0;
}
}
result = (result + (count * (count + 1) / 2) % mod) % mod;
return result;
}
}Try It Yourself
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