371

ruby/371-Sum-of-Two-Integers.rb

@@ -0,0 +1,42 @@
+def get_sum(a, b)
+ mask = 0xffffffff
+ until b.zero? # until no carries left
+ tmp = (a & b) << 1 # carries
+ a = (a ^ b) & mask # addition w/o carries
+ b = tmp & mask
+ end
+ a = ~(a ^ mask) if a > (mask >> 1)
+ a
+end
+
+# Ugly Solution
+def get_sum(a, b)
+ mask = 0xffffffff # 32 bit maximum
+ res = 0
+ carry = 0
+ 32.times do |n|
+ bit_a = (a >> n) & 1
+ bit_b = (b >> n) & 1
+
+ if (bit_a | bit_b).zero?
+ if carry == 1
+ carry -= 1
+ res |= (1 << n)
+ end
+ elsif (bit_a & bit_b) == 1
+ if carry == 1
+ res |= (1 << n)
+ else
+ carry += 1
+ end
+ elsif carry.zero?
+ res |= (1 << n)
+ end
+ end
+ res &= mask
+ if (res >> 31) & 1 == 1
+ # XOR flips rightmost 32, then NOT flips all bits
+ res = ~(res ^ mask)
+ end
+ res
+end