leetcode 696

696. Count Binary Substrings

First, I count the number of  or  grouped consecutively.

For example "" will be [, , , ].

Second, for any possible substrings with  and  grouped consecutively, the number of valid substring will be the minimum number of  and .

For example "", will be min(, ) = , ("", "", "")

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 int countBinarySubstrings(string s) {

        int cur = , pre = , res = ;

        for (int i = ; i < s.size(); i++) {

            if (s[i] == s[i - ]) cur++;

            else {

                res += min(cur, pre);  //主要是这里的技巧，比如"0001111", will be min(3, 4) = 3, ("01", "0011", "000111")

                pre = cur;

                cur = ;

            }

        }

        return res + min(cur, pre);

    }