現獲取道兩個字串長度最長的n，將char型別轉化為int型別，設定car來接收進位，然後迴圈之後，再判斷car是否為1，如果為1，用StringBuilde型別來接收，最後在反轉一下，呼叫toString方法返回。

package com.lhb.offer;

/**
 * @author lhb
 * @date 2022/3/16
 */
public class Offer_67 {
    static String sumTwo(String a, String b) {
        int n = Math.max(a.length(), b.length());
        
 
int ans = 0;
        int car = 0;
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < n; i++) {
            int va = i < a.length() ? (a.charAt(a.length() - i - 1) - '0') : 0;
            int vb = i < b.length() ? (b.charAt(b.length() - i - 1) - '0') : 0;
            car = car + va + vb;
            sb.append(car 
 
% 2);
            car = car / 2;
        }
        if (car == 1) {
            sb.append('1');
        }
        return sb.reverse().toString();
    }
    public static void main(String[] args) {
        String a = "1111";
        String b = "001";
        System.out.println(sumTwo(a, b));
    }
}