java中超过long范围的超大整数相加算法详解(面试高频)

package com.wandou.demo.algorithm.post;

import org.junit.Test;

/**
 * @author liming
 * @date 2020-08-19
 * @description 算法
 */
public class BigNumAddDemo {

  @Test
  public void bigintegerAddTest() {
    System.out.println("Long.MAX_VALUE = " + Long.MAX_VALUE);
    bigNumAdd("111", "2010");
    bigNumAdd(Long.MAX_VALUE + "", Long.MAX_VALUE + "");
    bigNumAdd(Long.MAX_VALUE + "", "10");
  }

  public void bigNumAdd(String strNum1, String strNum2) {
    char[] chars1 = strNum1.toCharArray();
    char[] chars2 = strNum2.toCharArray();
    int len1 = chars1.length;
    int len2 = chars2.length;
    boolean oneBiger = len1 > len2;
    int len = Integer.max(len1, len2);
    StringBuilder targetSb = new StringBuilder();
    //进位
    int carry = 0;
    for (int i = 0; i < len; i++) {
      int temp;
      int idx1 = len1 - 1 - i;
      int idx2 = len2 - 1 - i;
      if (oneBiger) {
        if (i < len2) {
          temp = Integer.parseInt(chars1[idx1] + "") + Integer.parseInt(chars2[idx2] + "") + carry;
        } else {
          temp = Integer.parseInt(chars1[idx1] + "") + carry;
        }
      } else {
        if (i < len1) {
          temp = Integer.parseInt(chars1[idx1] + "") + Integer.parseInt(chars2[idx2] + "") + carry;
        } else {
          temp = Integer.parseInt(chars2[idx2] + "") + carry;
        }
      }
      carry = 0;
      if (temp > 9) {
        carry = 1;
        targetSb.append(temp - 10);
      } else {
        targetSb.append(temp);
      }
    }
    System.out.println(targetSb.reverse().toString());
  }

}