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题目

• 原题连接：415. 字符串相加

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1- 思路

• 模式识别：字符串相加

逆向遍历过程模拟

• 数据结构 ① String res ：记录res 、② carry 记录进位值
• ① 定义两个整数遍历 nums1 和 nums2 ——>index1 = nums1.length,index2 - nums2.length
• ② 利用 while循环遍历 while( index1>=0 || index2>=0 || carry != 0)
• ③ 定义 x = index1>=0 ? nums1.charAt(i) - '0' : 0;
• 同理 y = index2>=0 ? nums1.charAt(i) - '0' : 0;
• 计算 int res = x+y+carry; 之后通过 StringBuffer ans = new StringBuffer(); sb.append(res%10)
• carry = res/10 ，之后 index1--; index2--;
• ④ 最终答案 revers

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2- 实现

⭐415. 字符串相加——题解思路

class Solution {
    public String addStrings(String num1, String num2) {
        int index1 = num1.length()-1;
        int index2 = num2.length()-1;

        int carry = 0;
        StringBuffer ans = new StringBuffer();
        // 逆向遍历
        while(index1>=0 || index2>=0  || carry!=0){
            int x = index1>=0 ? num1.charAt(index1) - '0' :0;
            int y = index2>=0 ? num2.charAt(index2) - '0' :0;
            int res = x+y+carry;
            ans.append(res%10);
            carry = res/10;
            index1--;
            index2--;
        }
        ans.reverse();
        return ans.toString();
    }
}

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3- ACM 实现

public class addString {


    public static String addTwo(String num1,String num2){
        int index1 = num1.length()-1;
        int index2 = num2.length()-1;

        int carry = 0;
        StringBuffer ans = new StringBuffer();
        // 遍历
        while( index1 >=0 || index2>= 0 || carry!=0){
            int x = index1>=0 ? num1.charAt(index1)-'0' : 0;
            int y = index2>=0 ? num2.charAt(index2)-'0' : 0;
            int res = x+y+carry;
            ans.append(res%10);
            carry = res/10;
            index1--;
            index2--;
        }
        ans.reverse();
        return ans.toString();
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        System.out.println("输入str1");
        String input1 = sc.next();
        System.out.println("输入str2");
        String input2 = sc.next();
        System.out.println("相加的结果是"+addTwo(input1,input2));
    }
}

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