43. Multiply Strings

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LeetCode

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class Solution {
    public String multiply(String num1, String num2) {
        int m =num1.length(), n=num2.length();
        int[] pos=new int[m+n];
        for(int i=m-1;i>=0;i--)
            for(int j=n-1;j>=0;j--){
                int multiplication=(num1.charAt(i)-'0')*(num2.charAt(j)-'0');
                int p1=i+j,p2=i+j+1;
                int sum=multiplication+pos[p2];
                
                pos[p2]=sum%10;
                pos[p1]+=sum/10;    
            }
        StringBuilder sb=new StringBuilder();
        for(int p:pos) if(!(sb.length()==0&&p==0)) sb.append(p);
        return sb.length()==0?"0":sb.toString();
    }
}
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