696. Count Binary Substrings

题目描述：

Give a string s, count the number of non-empty (contiguous) substrings that have the same number of 0's and 1's, and all the 0's and all the 1's in these substrings are grouped consecutively.

Substrings that occur multiple times are counted the number of times they occur.

思路一：

class Solution {
public int countBinarySubstrings(String s) {
if (s == null || s.length() == 0)
return 0;
int cnt = 0;
int preLength = 0;
int currLength = 1;
for (int i = 1; i < s.length(); i++)
{
if (s.charAt(i) == s.charAt(i - 1))
currLength++;
else
{
preLength = currLength;
currLength = 1;
}
if (preLength >= currLength)
cnt++;
}
return cnt;
}
}