371

Author: TedTran2019

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