大数运算（c、java）

最近看剑指offer的时候，看到c语言操作大数，于是就想用java来写写大数，小伙伴们都表示看不懂，

java有强大的BigInteger和BigDecimal类来支持大数的操作，可是，咸的蛋疼的人总是有的。

目前只完成了加减乘。

java代码

<span style="font-size:18px;">import java.util.Arrays;public class Test {// 将字符串转成整形数组static int[] StringToArray(String s) {int[] a = new int[s.length()];for (int i = 0; i < s.length(); i++) {a[i] = Integer.parseInt(s.substring(s.length() - i - 1, s.length()- i));}return a;}// 大数加法static int[] bigDataAdd(int[] a, int[] b) {if (a.length < b.length) {int[] temp = a;a = b;b = temp;}int len = a.length;// 多申请一位，存放进位int[] c = new int[len + 1];int flag = 0;// 判断是否进位for (int i = 0; i < b.length; i++) {c[i] = (a[i] + b[i] + flag) % 10;flag = (a[i] + b[i] + flag) / 10;}if (a.length == b.length && flag != 0) {c[len] = flag;} else {for (int i = b.length; i < a.length; i++) {c[i] = (a[i] + flag) % 10;flag = (a[i] + flag) / 10;}if (flag == 1) {c[len] = 1;}}return c;}// 加法打印结果static void printResult1(int[] result) {// 判断首位是否为0，为0不输出，不为0正常输出if (result[result.length - 1] == 0) {for (int i = result.length - 2; i >= 0; i--) {System.out.print(result[i]);}} else {for (int i = result.length - 1; i >= 0; i--) {System.out.print(result[i]);}}}// //将两个数组搞成等长的// static void equalLength(int[] a,int[] b){// int len = (a.length>b.length)?a.length:b.length;// a=Arrays.copyOf(a, len);// b=Arrays.copyOf(b, len);// // System.out.println(a.length+".."+b.length);// }// 大数减法：符号暂时没完成static int[] bigDataSubtract(int[] a, int[] b) {// 将a，b弄成同样长int len = (a.length > b.length) ? a.length : b.length;a = Arrays.copyOf(a, len);b = Arrays.copyOf(b, len);//System.out.println(a.length + ".." + b.length);int[] c = new int[len + 1];// 退位的标志位int flag = 0;for (int i = 0; i < len; i++) {c[i] = ((a[i] - flag) - b[i] + 10) % 10;//System.out.print(c[i] + "...");flag = (a[i] - flag) - b[i] >= 0 ? 0 : 1;}//System.out.println("c[len]=" + c[len]);if (flag == 0)return c;if (flag == 1) {//c[len] = 45;// 负号的int值为45return bigDataSubtract(b, a);}return c;}// 减法打印结果static void printResult2(int[] result) {System.out.println((char) result[result.length - 1]);if(result[result.length-2]==0){for (int i = result.length - 3; i >= 0; i--) {System.out.print(result[i]);}}else{for (int i = result.length - 2; i >= 0; i--) {System.out.print(result[i]);}}}// 乘法static int[] multiply(int a[], int b[]) {// 实现数组交换if (a.length < b.length) {int[] temp = a;a = b;b = temp;}int c[] = new int[a.length + b.length];int flag = 0;for (int j = 0; j < b.length; j++) {for (int i = 0; i < a.length; i++) {c[i + j] += a[i] * b[j];}}for (int i = 0; i < c.length; i++) {int temp = c[i];c[i] = (temp + flag) % 10;flag = (temp + flag) / 10;//System.out.println(c[i]);}return c;}//乘法打印static void printResult3(int[] result) {//System.out.println(result.length );System.out.println();if(result[result.length-1]!=0){for (int i = result.length-1; i >= 0; i--) {System.out.print(result[i]);}}else{for (int i = result.length-2; i >= 0; i--) {System.out.print(result[i]);}}}public static void main(String[] args) {int[] a = StringToArray("1800");int[] b = StringToArray("1300");int[] c1 = bigDataAdd(a, b);printResult1(c1);int[] c2 = bigDataSubtract(a, b);printResult2(c2);int[] c3 = multiply(a, b);printResult3(c3);}}</span>

<span style="font-size:18px;"></span>

BigInteger类实现大数操作

<span style="font-size:18px;">//java太强大了</span>

<span style="font-size:18px;">import java.math.BigInteger;class Test1{//加static void add(BigInteger bigInteger1,BigInteger bigInteger2){bigInteger1=bigInteger1.add(bigInteger2);System.out.println(bigInteger1);}//减static void subtract(BigInteger bigInteger1,BigInteger bigInteger2){bigInteger1=bigInteger1.subtract(bigInteger2);System.out.println(bigInteger1);}//乘static void multiply(BigInteger bigInteger1,BigInteger bigInteger2){bigInteger1=bigInteger1.multiply(bigInteger2);System.out.println(bigInteger1);}//除static void divide(BigInteger bigInteger1,BigInteger bigInteger2){bigInteger1=bigInteger1.divide(bigInteger2);System.out.println(bigInteger1);}//取反static void negate(BigInteger bigInteger1){bigInteger1=bigInteger1.negate();System.out.println(bigInteger1);}//阶乘static void pow(BigInteger bigInteger1,int n){bigInteger1=bigInteger1.pow(n);System.out.println(bigInteger1);}//取模static void remainder(BigInteger bigInteger1,BigInteger bigInteger2){bigInteger1 = bigInteger1.remainder(bigInteger2);System.out.println(bigInteger1);}public static void main(String[] args)throws Exception{BigInteger bigInteger1=new BigInteger("123214325345424");BigInteger bigInteger2=new BigInteger("5358038503535");add(bigInteger1,bigInteger2);subtract(bigInteger1,bigInteger2);multiply(bigInteger1,bigInteger2);divide(bigInteger1,bigInteger2);negate(bigInteger1);pow(bigInteger1,10);remainder(bigInteger1,bigInteger2);}}</span>

<strong><span style="font-size:18px;">c语言代码</span></strong>

<strong><span style="font-size:18px;"></span></strong><pre name="code" class="plain">#include<stdio.h>#include <string.h>#define M 10//大数加法void add(char s1[],char s2[])//参数为两个字符数组{//初始化int num1[M]={0};int num2[M]={0};int i,j;int len1=strlen(s1);int len2=strlen(s2);for(i=len1-1,j=0;i>=0;i--){num1[j++]=s1[i]-'0';}for(i=len2-1,j=0;i>=0;i--){num2[j++]=s2[i]-'0';}for(i=0;i<M;i++){num1[i]=num1[i]+num2[i];if(num1[i]>9){num1[i]=num1[i]-10;num1[i+1]++;}}//打印输出//找到第一个不是0的位置for(i=M-1;(i>=0)&&(num1[i]==0);i--);if(i>=0){for(;i>=0;i--)printf("%d",num1[i]);}else printf("0\n");}int compare(char* s1,char* s2){int sl1=strlen(s1);int sl2=strlen(s2);if(sl1>sl2)return 1;else if(sl1<sl2)return -1;else{int i=0;while(i<sl1-1){if(s1[i]>s2[i]){return 1;}else if(s1[i]<s2[i]){return -1;}else{i++;}}return 0;}}//大数减法void subtract(char s1[],char s2[]){//初始化int num1[M]={0};int num2[M]={0};int i,j;int len1=strlen(s1);int len2=strlen(s2);for(i=len1-1,j=0;i>=0;i--){num1[j++]=s1[i]-'0';}for(i=len2-1,j=0;i>=0;i--){num2[j++]=s2[i]-'0';}int flag=compare(s1,s2);if(flag>=0){for(i=0;i<M;i++){num1[i]=num1[i]-num2[i];if(num1[i]<0){num1[i]=num1[i]+10;num1[i+1]--;}}for(i=M-1;(i>=0)&&(num1[i]==0);i--);if(i>=0){for(;i>=0;i--)printf("%d",num1[i]);}else printf("0\n");}else{for(i=0;i<M;i++){num2[i]=num2[i]-num1[i];//printf("%d",num2[i]);if(num2[i]<0){num2[i]=num2[i]+10;num2[i+1]--;}}for(i=M-1;(i>=0)&&(num2[i]==0);i--);printf("-");if(i>=0){for(;i>=0;i--)printf("%d",num2[i]);}else printf("0\n");}}void Multiply(char s1[],char s2[]){//初始化int num1[M]={0};int num2[M]={0};int num3[M]={0};int i,j;int len1=strlen(s1);int len2=strlen(s2);for(i=len1-1,j=0;i>=0;i--){num1[j++]=s1[i]-'0';}for(i=len2-1,j=0;i>=0;i--){num2[j++]=s2[i]-'0';}for(j=0;j<len2;j++){for(i=0;i<len1;i++){num3[i+j]+=num1[i]*num2[j];}}//printf("%d\n",num3[0]);int flag=0;for(i=0;i<M;i++){int p=num3[i];num3[i]=(p+flag)%10;flag=(p+flag)/10;}for(i=M-1;(i>=0)&&(num3[i]==0);i--){}if(i>=0){for(;i>=0;i--){printf("%d",num3[i]);}}else//没有打印0printf("0\n");}<span style="color:#ff0000;">//注意定义char类型的字符串方式</span>void main(){//char s1[]={'1','2','\0'};char s1[]="10000";char s2[]="982323";Multiply(s1,s2);}

总结：java减法一直是困扰我的，因为符号判断很难，策略：1.看长度，但如果长度相同呢，2.只能先运行一遍再判断最高位是否退位了，退位了加负号，这么简单的还是没完成。