CareerCup

/*
i1 * i2
int result = 0;
add i1 to result i2 times.
*/

public int multiple (int i1, int i2) {
 int i = 0;
 int result = 0;
 while (i2 > i) {
  result = add(result, i1);
  i = add(i, 1);
 }
 return result;
}

public int add(int i1, int i2) {
 // iterate until there is no carry
 while (i2 != 0) {
  // carry contains common set bits of i1 and i2
  int carry = i1 & i2;
  // sum of bits of i1 and i2 where at least either of i1 and i2 bits is 0
  i1 = i1 ^ i2;
  // carry is shifted by one so that adding it to i1 gives the required sum
  i2 = carry << 1;
 }
 return i1;
}

Below method should work:

public static int mulipleCustomLooping(int a, int b) {

int getresultat = 0;
for (int i = 0; i < a; i++) {
getresultat += b;
}

return getresultat;
}

public static int mulipleCustomLooping(int a, int b) {
int getresultat = 0;
for (int i = 0; i < a; i++) {
getresultat += b;
}
return getresultat;
}

public static int multiply(int i1, int i2) {
        boolean isPositive = false;

        if(i1==0 || i2==0) return 0;

        if(i1<0 & i2<0) isPositive=true;
        else if(i1>0 & i2>0) isPositive=true;

        if(i1<0) i1 = ~i1+1;
        if(i2<0) i2 = ~i2+1;

        int acc = i1;

        for(int i=2; i <= i2; i++) acc = add(acc, i1);
        return isPositive ? acc : ~acc+1;
    }

public static int add(int i1, int i2){
        final int mask = 1;

        int subsum=0, result=0, pos=0;
        boolean carryOver=false;

        while(i1>=0 || i2>=0){
            final int digitA = i1 & mask, digitB = i2 & mask;

            /*
                0 ^ 0 = 0
                0 ^ 1 = 1
                1 ^ 0 = 1
                1 ^ 1 = 0
             */

            subsum = digitA ^ digitB;

            if(carryOver) subsum ^= 1;

            carryOver = (carryOver && (digitA == 1 || digitB == 1)) |
                    (!carryOver && digitA == digitB && digitB == 1);

            i1 >>= 1; i2 >>= 1;
            subsum <<= pos;
            pos++;
            result |= subsum;

            if(i1 == i2 && i2 == 0 && !carryOver) break;;
        }

        return result;
    }

Here is my approach -:

int ans = 0;
     for(i=0;i<a;i++)
     {
           ans = ans xor b + (ans && b) << 1;
     }

public static int multiply(int a,int b){
// flag to store if result is positive or negative
boolean isNegative = false;

// if both numbers are negative, make both numbers
// positive as result will be positive anyway
if (a < 0 && b < 0) {
a = -a;
b = -b;
}

// if only a is negative, make it positive
// and mark result as negative
if (a < 0) {
a = -a;
isNegative = true;
}

// if only b is negative, make it positive
// and mark result as negative
if (b < 0) {
b = -b;
isNegative = true;
}
int res =0;
// While second number doesn't become 1
while (b!=0){

// If second number becomes odd,
// add the first number to result
if((b&1)!=0){
res +=a;
}
// Double the first number
// and halve the second number
a = a <<1;
b = b >>1;
}
return (isNegative) ? -res : res;
}

public static int multiply(int a,int b){
        // flag to store if result is positive or negative
        boolean isNegative = false;

        // if both numbers are negative, make both numbers
        // positive as result will be positive anyway
        if (a < 0 && b < 0) {
            a = -a;
            b = -b;
        }

        // if only a is negative, make it positive
        // and mark result as negative
        if (a < 0) {
            a = -a;
            isNegative = true;
        }

        // if only b is negative, make it positive
        // and mark result as negative
        if (b < 0) {
            b = -b;
            isNegative = true;
        }
            int res =0;
        // While second number doesn't become 1
            while (b!=0){

                // If second number becomes odd,
                // add the first number to result
                if((b&1)!=0){
                    res +=a;
                }
                // Double the first number
                // and halve the second number
                a = a <<1;
                b = b >>1;
            }
        return (isNegative) ? -res : res;
    }