高精度乘

高精度乘，和我们小学的手算一样

 

这里只需要注意进位就行

 

#include<cstdio>
#include<cmath>
#include<algorithm>
#include<cstring>
#include<iostream>
using namespace std;
char s1[10005],s2[10005];
int ll[10005];
int len1,len2,len3;
int main() {
    freopen("t.in","r",stdin);
    freopen("t.out","w",stdout);
    memset(ll,0,sizeof(ll));
    scanf("%s",s1);
    scanf("%s",s2);
    len1 = strlen(s1);
    len2 = strlen(s2);
    for(int i=0; i<=(len1-1)/2; i++) {
        char c = s1[i];
        s1[i] = s1[len1-i-1];
        s1[len1-i-1] = c;
    }
    for(int i=0; i<=(len2-1)/2; i++) {
        char c = s2[i];
        s2[i] = s2[len2-i-1];
        s2[len2-i-1] = c;
    }
    for(int i=0; i<len1; i++) {
        for(int j=0; j<len2; j++) {
            ll[j+i] += (s1[i]-'0')*(s2[j]-'0');
        }
    }
    len3 = len1+len2-1;
    for(int i=0; i<len3; i++) {
        while(ll[i]>=10) {
            ll[i]-=10;
            ll[i+1]++;
        }
    }
    if(ll[len3]>0) len3++;
    int i = len3-1;
    while(i>0) {
        if(ll[i]!=0) break;
        i--;
    }
    len3 = i;
    for(int i=len3; i>=0; i--) {
        printf("%d",ll[i]);
    }
    return 0;
}