Multiply Strings (Medium)

Description

Given two numbers represented as strings, return multiplication of the numbers as a string.

Note: The numbers can be arbitrarily large and are non-negative.

Analysis

模拟大数乘法= =。

My Solution

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//C
char* multiply(char* num1, char* num2) {
    int len1 = strlen(num1),len2 = strlen(num2),len;
    char *ans = (char *)malloc(sizeof(char)*(len1+len2+2));
    char  t ;
    for(int i = 0;i<len1/2;i++){
        t = num1[i];
        num1[i]=num1[len1-i-1];
        num1[len1-i-1] = t;
    }
    for(int i = 0;i<len2/2;i++){
        t = num2[i];
        num2[i]=num2[len2-i-1];
        num2[len2-i-1] = t;
    }
    for(int i = 0;i<len1+len2+1;i++){
        ans[i] = 0;
    }
    for(int i = 0;i<len1;i++){
        for(int j = 0;j<len2;j++){
            ans[i+j]+=(num1[i]-'0')*(num2[j]-'0');
            ans[i+j+1]+=ans[i+j]/10;
            ans[i+j]%=10;
        }
    }
    len = len1 + len2;
    while(len-1>0&&!ans[len-1])
        len--;
    for(int i = 0;i<len/2;i++){
        t = ans[i];
        ans[i]=ans[len-i-1];
        ans[len-i-1] = t;
    }
    for(int i = 0;i<len;i++){
        ans[i]+='0';
    }
    ans[len]=0;
    return ans;
}