• 在Java中有专门处理高精度的API：BigInteger和BigDecimal，所以在Java中不用对大整数进行专门的处理，相应的用法和底层原理请详见我的两篇笔记

  • Java BigInteger：juejin.cn/post/716030…
  • Java BigDecimal：juejin.cn/post/716065…

模板

• C++

// C = A + B, A >= 0, B >= 0
vector<int> add(vector<int> &A, vector<int> &B)
{
    if (A.size() < B.size()) return add(B, A);

    vector<int> C;
    int t = 0;
    for (int i = 0; i < A.size(); i ++ )
    {
        t += A[i];
        if (i < B.size()) t += B[i];
        C.push_back(t % 10);
        t /= 10;
    }

    if (t) C.push_back(t);
    return C;
}

• Java

public static List<Integer> add(List<Integer> num1, List<Integer> num2) {
        if (num1.size() < num2.size()) {
            return add(num2, num1);
        }
        List num3 = new ArrayList<>();
        int t = 0;
        for (int i = 0; i < num1.size() || t != 0; i++) {
            if (i < num1.size()) {
                t += num1.get(i);
            	if (i < num2.size()) {
                	t += num2.get(i);
            	}
            }
            num3.add(t % 10);
            t /= 10;
        }
        return num3;
    }

练习

01 高精度加法

• 题目

• 题解

import java.io.*;
import java.util.*;

public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        char[] chars1 = br.readLine().toCharArray();
        List<Integer> num1 = new ArrayList<>();
        for (int i = chars1.length - 1; i >= 0; i--) {
            num1.add(chars1[i] - '0');
        }
        char[] chars2 = br.readLine().toCharArray();
        List<Integer> num2 = new ArrayList<>();
        for (int i = chars2.length - 1; i >= 0; i--) {
            num2.add(chars2[i] - '0');
        }
        br.close();
        List<Integer> num3 = add(num1, num2);
        for (int i = num3.size() - 1; i >= 0; i--) {
            System.out.print(num3.get(i));
        }
    }

    public static List<Integer> add(List<Integer> num1, List<Integer> num2) {
        if (num1.size() < num2.size()) {
            return add(num2, num1);
        }
        List num3 = new ArrayList<>();
        int t = 0;
        for (int i = 0; i < num1.size() || t != 0; i++) {
            if (i < num1.size()) {
                t += num1.get(i);
                if (i < num2.size()) {
                    t += num2.get(i);
                }
            }
            num3.add(t % 10);
            t /= 10;
        }
        return num3;
    }
}

import java.io.*;
import java.math.*;

public class highprecisionaddition2 {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        BigInteger num1 = new BigInteger(br.readLine());
        BigInteger num2 = new BigInteger(br.readLine());
        br.close();
        System.out.println(num1.add(num2));
    }
}