Product of Array Exclude Itself

Given an integers array A.

Define B[i] = A[0] * … * A[i-1] * A[i+1] * … * A[n-1], calculate B WITHOUT divide operation.

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Example

For A = [1, 2, 3], return [6, 3, 2].

public class Solution {
/**
* @param A: Given an integers array A
* @return: A Long array B and B[i]= A[0] * ... * A[i-1] * A[i+1] * ... * A[n-1]
*/
public ArrayList<Long> productExcludeItself(ArrayList<Integer> A) {
// write your code
ArrayList<Long> res = new ArrayList<Long>();
if (A==null || A.size()==0 ) return res;
long[] lProduct = new long[A.size()];
long[] rProduct = new long[A.size()];
lProduct[0] = 1;
for (int i=1; i<A.size(); i++) {
lProduct[i] = lProduct[i-1]*A.get(i-1);//left 累×
}
rProduct[A.size()-1] = 1;//right 累×
for (int j=A.size()-2; j>=0; j--) {
rProduct[j] = rProduct[j+1]*A.get(j+1);
}
for (int k=0; k<A.size(); k++) {
res.add(lProduct[k] * rProduct[k]);
}
return res;
}
}