Google Interview Question for Software Engineers


Country: UK
Interview Type: Phone Interview




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1
of 1 vote

public String bigSum(String s1, String s2) {
        int lengthS1 = s1.length();
        int lengthS2 = s2.length();

        int diff = Math.abs(lengthS1 - lengthS2);

        StringBuilder prefix = new StringBuilder();
        for (int i = 0; i < diff; i ++) {
            prefix.append("0");
        }

	//Normilise the length
        if (lengthS1 < lengthS2) {
            s1 = prefix + s1;
        } else if (lengthS2 < lengthS1) {
            s2 = prefix + s2;
        }

        StringBuilder out = new StringBuilder();
        int buf = 0;
        for (int i = s1.length() - 1; i >= 0; i--) {
            int n1 = Integer.parseInt(String.valueOf(s1.charAt(i)));
            int n2 = Integer.parseInt(String.valueOf(s2.charAt(i)));

            int sum = buf + n1 + n2;
            buf = 0;
            if (sum >= 10) {
                sum = sum % 10;
                buf++;
            } else {
                buf = 0;
            }

            out.insert(0, sum);
        }


        return out.toString();
    }

- Denys February 12, 2018 | Flag Reply
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0
of 0 votes

Continue to the answer above.

Tested with the UT:
assertEquals("0", codeBase.bigSum("909876545678909876878765546789765490987654567890987687876554678976546789909876545678909876878765546789765467890876545678908765457890087654567890876545789067899098765456789098768787655467897654678908765456789087654578900876545678908765457890", "909876545678909876878765546789765490987654567890987687876554678976546789909876545678909876878765546789765467890876545678908765457890087654567890876545789067899098765456789098768787655445678908765457890"));

- denis.zayats February 12, 2018 | Flag
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0
of 0 vote

you have to multiply the numbers..not add them..

- anon February 13, 2018 | Flag Reply
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0
of 0 vote

Cheers Denys,

The question was aiming for Mul = Multiply rather thank Sum :)

- NA February 13, 2018 | Flag Reply
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0
of 0 vote

Here is the multiplication. The method "bigSum" is described above.
The function works only with an equal Strings by length.

unit test:
bigMultipl("123456781234567812345678123456781231234567812345678123456781234567812345678123456781234567812345678123456781234567812345678123456781234567812345678123456781234567812345678123456781234567812345678456781234567812345678123456781234567812345678",

"123456781234567812345678123456781231234567812345678123456781234567812345678123456781234567812345678123456781234567812345678123456781234567812345678123456781234567812345678123456781234567812345678456781234567812345678123456781234567812345678"));

result =
15241566832799835131840019356816873129412161060136908261522059216750369293320360971620290100369704845365086870331252870116370369202120372405370527895373317370413557870939420377432620454710371351027673886100984519252301774947583571499390156842912823863303992974797473165550166654279282375988982091851404238129875577457087736154196977375165932083620904155824874754407079505654114672374342882186495595263426186618964206036665458836888572988923249505065691208988873673208352565279684

public String bigMultipl(String s1, String s2) {
        LinkedList<String> list = new LinkedList<>();
        int lengthS1 = s1.length();
        int lengthS2 = s2.length();

        int diff = Math.abs(lengthS1 - lengthS2);

        StringBuilder prefix = new StringBuilder();
        for (int i = 0; i < diff; i++) {
            prefix.append("0");
        }


        if (lengthS1 < lengthS2) {
            s1 = prefix + s1;
        } else if (lengthS2 < lengthS1) {
            s2 = prefix + s2;
        }
        for (int i = s1.length() - 1; i >= 0; i --) {
            int buf = 0;
            String tempSum = "";
            for (int j = s2.length() - 1; j >= 0; j --) {
                int n1 = Integer.parseInt(String.valueOf(s1.charAt(i)));
                int n2 = Integer.parseInt(String.valueOf(s2.charAt(j)));

                int sum = buf + n1 * n2;
                buf = 0;
                if (sum >= 10) {
                    buf += sum / 10;
                    sum = sum % 10;
                } else {
                    buf = 0;
                }
                tempSum = String.valueOf(sum) + tempSum;

            }
            if (buf > 0) {
                list.add(buf + tempSum);
            } else {
                list.add(tempSum);
            }
        }

        String sum = "";
        for (int i = 0; i < list.size(); i ++) {
            sum = bigSum(sum, list.get(i) + repeatString("0", i));
        }

        if (sum.startsWith("0")) {
            sum = "1" + sum;
        }

        return sum;
    }

- denis.zayats February 13, 2018 | Flag Reply
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0
of 0 vote

public static String mul(String l, String r) {
    if (l == null || l.equals("0") || r == null || r.equals("0")) {
        return "0";
    }

    boolean isNegative = false;
    if (l.startsWith("-")) {
        isNegative = true;
        l = l.substring(1);
    }

    if (r.startsWith("-")) {
        isNegative ^= true;
        r = r.substring(1);
    }

    int[] result = new int[l.length() + r.length()];
    int resultEnd = result.length - 1;
    int resultIdx = 0;

    for (int rightIdx = r.length() - 1; rightIdx >= 0; rightIdx--) {
        int carry = 0;
        resultIdx = resultEnd;

        for (int leftIdx = l.length() - 1; leftIdx >= 0; leftIdx--) {
            int curr = (l.charAt(leftIdx) - '0') * (r.charAt(rightIdx) - '0')
                    + carry + result[resultIdx];
            result[resultIdx--] = curr % 10;
            carry = curr / 10;
        }

        if (carry > 0) {
            result[resultIdx] = carry;
        }

        resultEnd--;
    }

    StringBuilder sb = new StringBuilder();
    if (isNegative) sb.append("-");

    if (result[resultIdx] == 0) resultIdx++;
    for (int i = resultIdx; i < result.length; i++) {
        sb.append(result[i]);
    }

    return sb.toString();
}

- jgriesser February 13, 2018 | Flag Reply
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0
of 0 vote

+ (NSString *)mulS1:(NSString *)s1 withS2:(NSString *)s2
{
NSString *result = [NSString new];
NSMutableString *tempResult;

NSInteger temp = 0;
NSInteger carry = 0;

for (NSInteger i = [s1 length] - 1; i >= 0; i--) {
tempResult = [NSMutableString new];
for (NSInteger j = [s2 length] - 1; j >= 0; j--) {
temp = ([s1 characterAtIndex:i] - '0') * ([s2 characterAtIndex:j] - '0') + carry;
carry = temp / 10;
[tempResult insertString:[@(temp % 10) stringValue] atIndex:0];
}
[tempResult insertString:[@(carry) stringValue] atIndex:0];
carry = 0;
if ([s1 length] - i - 1 > 0) {
[tempResult appendString:[[@(pow(10, [s1 length] - 1 - i)) stringValue] substringFromIndex:1]];
}
result = [self sumS1:result withS2:[tempResult copy]] ;
}
return result;
}

+ (NSString *)sumS1:(NSString *)s1 withS2:(NSString *)s2
{
NSInteger temp = 0;
NSInteger carry = 0;
NSMutableString *result = [NSMutableString new];
for (NSInteger i = 0; i <= MAX([s1 length], [s2 length]); i++) {
temp = (i < [s1 length] ? [s1 characterAtIndex:[s1 length] - i - 1] - '0' : 0) + (i < [s2 length] ? [s2 characterAtIndex:[s2 length] - i - 1] - '0' : 0) + carry;
carry = temp / 10;
[result insertString:[@(temp % 10) stringValue] atIndex:0];
}
return [result copy];
}

- Madhur February 20, 2018 | Flag Reply
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0
of 0 vote

String function(String s1, String s2) {
        if (s1 == null || s1?.isEmpty() || s2 == null || s2?.isEmpty())
            throw new Exception("Please input the valid strings. Current input strings are \"$s1\" and \"$s2\"")

        ArrayList<Objects> analyzedNumbers = analyzeNumbers(s1, s2)
        boolean negativeSign = analyzedNumbers.get(2)

        int sizeNum1 = s1.size()
        int sizeNum2 = s2.size()
        Stack<Character> num1 = sizeNum1 <= sizeNum2 ? analyzedNumbers.get(0).split('') : analyzedNumbers.get(1).split('')
        Stack<Character> num2 = sizeNum1 <= sizeNum2 ? analyzedNumbers.get(1).split('') : analyzedNumbers.get(0).split('')

        int mulRemainder = 0, i = 0

        int[][] matrix = (sizeNum1 > sizeNum2) ? new int[sizeNum1 + sizeNum2][sizeNum2] : new int[sizeNum1 + sizeNum2][sizeNum1]

        for (i; num1.size() > 0; i++) {
            Stack<String> cloneNum2 = (Stack<String>) num2.clone()
            String multiplier1 = num1.pop()
            int j = i

            for (j; cloneNum2.size() > 0; j++) {
                String multiplier2 = cloneNum2.pop()
                if (multiplier1 == '0' || multiplier2 == '0') {
                    matrix[j][i] = mulRemainder
                    mulRemainder = 0
                } else {
                    try {
                        mulRemainder += multiplier1.toInteger() * multiplier2.toInteger()
                    } catch (NumberFormatException ex) {
                        throw new Exception("Please input the valid strings. Current input strings are \"$s1\" and \"$s2\"")
                    }
                    if (mulRemainder > 9) {
                        matrix[j][i] = mulRemainder % 10
                        mulRemainder = mulRemainder / 10
                    } else {
                        matrix[j][i] = mulRemainder
                        mulRemainder = 0
                    }
                    if (cloneNum2.size() == 0) {
                        matrix[++j][i] = mulRemainder
                        mulRemainder = 0
                    }
                }
            }
        }

        StringBuilder res = calculateResult(matrix)

        while (res.substring(res.length() - 1) == '0')
            res.deleteCharAt(--res.length())

        negativeSign ? res.append('-').toString() : res.toString()
        res.reverse()
    }

    private static StringBuilder calculateResult(int[][] inputMatrix) {
        StringBuilder res = new StringBuilder()
        int sumRemainder = 0

        for (int n = 0; n < inputMatrix.length; n++) {
            int sum = sumRemainder
            for (int m = 0; m < inputMatrix[n].length; m++) {
                sum += inputMatrix[n][m]
            }
            if (sum > 9) {
                sumRemainder = sum / 10
                sum = sum % 10
            } else {
                sumRemainder = 0
            }
            res.append(sum)
        }
        res
    }

    private static ArrayList<Objects> analyzeNumbers(String str1, String str2) {
        ArrayList<Objects> result = new ArrayList<>()
        boolean negativeFirstVar = str1.startsWith('-')
        boolean negativeSecondVar = str2.startsWith('-')

        result.add(negativeFirstVar ? str1.substring(1) : str1)
        result.add(negativeSecondVar ? str2.substring(1) : str2)
        result.add(negativeFirstVar ^ negativeSecondVar)
        result
    }

function('247', '384') == '94848'
function('-247655', '-44') == '10896820'
function('10265893', '-3658156') == '-37554238073308' 
       function('894761335465132123543696666635453102658931546541536555555555554654145341343', '-952000000000000133214564352154352456432156453143658156') == '-851812791362805900808840729776363087775056644562160840739403170545129605964203662825133780128500820674736147406436873872325943508'
function('','') throw java.lang.Exception: Please input the valid strings.
function(null,'')  throw java.lang.Exception: Please input the valid strings.
function(null,null)  throw java.lang.Exception: Please input the valid strings.
function('','1sdf56')  throw java.lang.Exception: Please input the valid strings.
function('',null)  throw java.lang.Exception: Please input the valid strings.

- Natalia March 14, 2018 | Flag Reply


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