1003

class Solution {
public:
    bool isValid(string s) {
        int i, j;
        for(i=0, j=0; j<s.length(); i++, j++){
            s[i] = s[j];
            if(i >= 2 && s[i] == 'c' && s[i-1] == 'b' && s[i-2] == 'a')
                i -= 3;
        }
        return i ? false : true;
    }
};