A question on StackExchange [1]:
"
I was asked the following interview question over the phone:
Given an array of integers, produce an array whose values
are the product of every other integer excluding the current index.
Example:
[4, 3, 2, 8] -> [3*2*8, 4*2*8, 4*3*8, 4*3*2] -> [48, 64, 96, 24]
"
His answer is given in the postscript. It spans 3 kilobytes over 86 lines.
The community's responses aren't much of an improvement (by that metric;
by other metrics - Java-specific ones, they decent advancements).
The J answer?
1 */\. 4 3 2 8
48 64 96 24
Could've answered the interviewer in a sentence, right over the phone.
-Dan
[1] Code Review StackExchange question
"Array whose values are the product of every other integer":
http://codereview.stackexchange.com/questions/45498/array-whose-values-are-the-product-of-every-other-integer
import java.math.BigInteger;
import java.util.Arrays;
public class ProductOfAnArray {
public static void main(String[] args) {
try {
System.out.println(Arrays.toString(ProductOfAnArray
.calcArray(new int[] { 4, 3, 2, 8 })));
System.out.println(Arrays.toString(ProductOfAnArray
.calcArray(new int[] { 4, 0, 2, 8 })));
System.out.println(Arrays.toString(ProductOfAnArray
.calcArray(new int[] { 4, 0, 2, 0 })));
System.out.println(Arrays.toString(ProductOfAnArray
.calcArray(new int[] {})));
System.out
.println(Arrays.toString(ProductOfAnArray
.calcArray(new int[] { 4, 3, 2, 8, 3, 2, 4, 6,
7,
3, 2, 4 })));
System.out
.println(Arrays.toString(ProductOfAnArray
.calcArray(new int[] { 4, 3, 2, 8, 3, 2, 4, 6,
7,
3, 2, 4 })));
System.out.println(Arrays.toString(ProductOfAnArray
.calcArray(new int[] { 4432432, 23423423, 34234,
23423428,
4324243, 24232, 2342344, 64234234, 4324247,
4234233, 234422, 234244 })));
} catch (Exception e) {
// debug exception here and log.
}
}
/*
* Problem: Given an array of integers, produce an array whose values
are
* the product of every other integer excluding the current index.
*
* Assumptions. Input array cannot be modified. input is an integer
array
* "produce an array" - type not specified for output array
*
* Logic explanation:
*
* Assume we have array [a,b,c,d] Let multiple be multiple of each
element
* in array. Hence multiple = 0 if one of the element is 0; To produce
the
* output. Ans at i -> multiple divided by the value at i. if 2 numbers
are
* 0 then entire output will be 0 because atleast one 0 will be a
multiple
* if 1 number is 0 then every thing else will be 0 except that index
whole
* value is to be determined
*
*/
public static BigInteger[] calcArray(final int[] inp) throws Exception {
if (inp == null)
throw new Exception("input is null");
int cnt = 0;
BigInteger multiple = new BigInteger("1");
boolean foundZero = false;
for (int i : inp) {
if (i == 0) {
cnt++;
foundZero = true;
if (cnt < 2)
continue;
else
break;
}
multiple = multiple.multiply(BigInteger.valueOf(i));
}
BigInteger ans[] = new BigInteger[inp.length];
for (int i = 0; i < inp.length; i++) {
if (foundZero) {
if (cnt < 2) {
ans[i] = (inp[i] == 0) ? multiple : new BigInteger("0");
} else {
ans[i] = new BigInteger("0");
}
} else {
ans[i] = multiple.divide(BigInteger.valueOf(inp[i]));
}
}
return ans;
}
}
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