LeetCode - 67. Add Binary(4ms)

Given two binary strings, return their sum (also a binary string).

The input strings are both non-empty and contains only characters 1 or 0.

Example 1:

Input: a = "11", b = "1"
Output: "100"

Example 2:

Input: a = "1010", b = "1011"
Output: "10101"

 class Solution {
 public:
     string addBinary(string a, string b) {
         int la = a.length();
         int lb = b.length();
         string res = "";
         int car = ;
         if(la <= lb) {
             for(int i = la - ; i >= ; i--) {
                 if(a[i] == '' && b[lb - (la - i)] == '') {
                     if(car == )
                         res = '' + res;
                     else {
                         res = '' + res;
                         car = ;
                     }
                 }
                 else if(a[i] != b[lb - (la - i)]) {
                     if(car == )
                         res = '' + res;
                     else
                         res = '' + res;
                 }
                 else {
                     if(car == ) {
                         res = '' + res;
                         car = ;
                     }
                     else
                         res = '' + res;
                 }
             }
             for(int i = lb - la - ; i >= ; i--) {
                 if(b[i] == '') {
                     if(car == )
                         res = '' + res;
                     else
                         res = '' + res;
                 }
                 else {
                     if(car == ) {
                         res = '' + res;
                         car = ;
                     }
                     else
                         res = '' + res;
                 }
             }
             if(car == ) {
                 res = '' + res;
             }
             return res;
         }
         else if(lb < la) {
             for(int i = lb - ; i >= ; i--) {
                 if(b[i] == '' && a[la - (lb - i)] == '') {
                     if(car == )
                         res = '' + res;
                     else {
                         res = '' + res;
                         car = ;
                     }
                 }
                 else if(b[i] != a[la - (lb - i)]) {
                     if(car == )
                         res = '' + res;
                     else
                         res = '' + res;
                 }
                 else {
                     if(car == ) {
                         res = '' + res;
                         car = ;
                     }
                     else
                         res = '' + res;
                 }
             }
             for(int i = la - lb - ; i >= ; i--) {
                 if(a[i] == '') {
                     if(car == )
                         res = '' + res;
                     else
                         res = '' + res;
                 }
                 else {
                     if(car == ) {
                         res = '' + res;
                         car = ;
                     }
                     else
                         res = '' + res;
                 }
             }
             if(car == ) {
                 res = '' + res;
             }
             return res;
         }
     }
 };