leetcode/67.cpp at master · joey11121/leetcode · GitHub

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class Solution {
public:
    string addzero(string s, int len1, int len2){
        string t;
        for(int i = 0; i < len1 - len2; i++){
            t.insert(0, "0");
        }
        t.append(s, 0, len2);
        return t;
    }
    string addBinary(string a, string b) {
        int alen = a.size(), blen = b.size(), len;
        int i, j;
        bool carryout = 0;
        string c;   //The answer that we need to return;
        if(alen > blen){
            b = addzero(b, alen, blen);
            len = alen;
        }
        else if(blen > alen){
            a = addzero(a, blen, alen);
            len = blen;
        }
        else{
            len = alen;
        }
        for(i = len - 1; i >= 0; i--){
            if(a.at(i) == '0' && b.at(i) == '0'){
                if(carryout == 1){
                    c.insert(0, "1");
                }else{
                    c.insert(0, "0");
                }
                carryout = 0;
            }
            if((a.at(i) == '1' && b.at(i) == '0') || (a.at(i) == '0' && b.at(i) == '1')){
                if(carryout == 1){
                    c.insert(0, "0");
                    carryout = 1;
                }else{
                    c.insert(0, "1");
                    carryout = 0;
                }
            }
            if(a.at(i) == '1' && b.at(i) == '1'){
                if(carryout == 1){
                    c.insert(0, "1");
                }else{
                    c.insert(0, "0");
                }
                carryout = 1;
            }
        }
        if(carryout == 1)
            c.insert(0, "1");

        return c;
    }
};