29. Divide Two Integers

Thinking:

• Method1: Search We need to find if (target - current) is in the set, if not, add current to a hashSet for checking. Since to need to return the index according to value, so the key is value of number and value is index of number in array.

    class Solution {
        public int divide(int dividend, int divisor) {
            int sign = 1;
            if((dividend > 0 && divisor< 0) || (dividend < 0 && divisor > 0))   sign = -1;
            Long ldividend = Math.abs((long)dividend);
            Long ldivisor = Math.abs((long)divisor);
            if(ldividend < ldivisor) return 0;
            long result = divide(ldividend, ldivisor);
            if(result > Integer.MAX_VALUE)  return (sign == 1)?Integer.MAX_VALUE:Integer.MIN_VALUE;
            return (int)((sign == 1)?result:-result);
        }
  
        private long divide(long ldividend, long ldivisor){
            if(ldividend < ldivisor) return 0;
            long sum = ldivisor;
            long result = 1;
            while((sum + sum) < ldividend){
                sum += sum;
                result += result;
            }
            return result + divide(ldividend - sum , ldivisor);
        }
    }