ARST打卡第341周

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class Solution {
public:
    int numSub(string s) {
        int n = s.size();
        int ans = 0;
        const int MOD = 1e9 + 7;
        for (int i = 0; i < n; i++) {
            if (s[i] == '1') {
                int len = 0;
                while (i < n && s[i] == '1') {
                    len++;
                    i++;
                }
                // long long 和提前取模防止溢出
                ans = (ans + (long long)len * (len + 1) / 2 % MOD) % MOD;
            }
        }
        return ans;
    }
};