Solution 007 013 and 014 using Ruby

Author: MarkKuang1991

solution/007.Reverse Integer/Solution.rb

@@ -0,0 +1,21 @@
+# @param {Integer} x
+# @return {Integer}
+def reverse(x)
+  neg = x < 0
+
+  x = x.abs
+  s = ''
+
+  x /= 10 while x > 0 && (x % 10).zero?
+
+  while x > 0
+    s += (x % 10).to_s
+    x /= 10
+  end
+
+  s = neg ? '-' + s : s
+
+  # have to explicitly constraint the int boundary as per the dummy test case
+  res = s.to_i
+  res <= 214_748_364_7 && res >= -214_748_364_8 ? res : 0
+end

solution/013.Roman to Integer/Solution.rb

@@ -0,0 +1,32 @@
+# @param {String} s
+# @return {Integer}
+def roman_to_int(s)
+  hash = Hash[
+      'I' => 1,
+      'V' => 5,
+      'X' => 10,
+      'L' => 50,
+      'C' => 100,
+      'D' => 500,
+      'M' => 1000,
+      'IV' => 4,
+      'IX' => 9,
+      'XL' => 40,
+      'XC' => 90,
+      'CD' => 400,
+      'CM' => 900
+  ]
+  res = 0
+  i = 0
+  while i < s.length
+    if i < s.length - 1 && !hash[s[i..i+1]].nil?
+      res += hash[s[i..i+1]]
+      i += 2
+    else
+      res += hash[s[i]]
+      i += 1
+    end
+  end
+
+  res
+end

solution/014.Longest Common Prefix/Solution.rb

@@ -0,0 +1,25 @@
+# @param {String[]} strs
+# @return {String}
+def longest_common_prefix(strs)
+  return '' if strs.nil? || strs.length.zero?
+
+  return strs[0] if strs.length == 1
+
+  idx = 0
+  while idx < strs[0].length
+    cur_char = strs[0][idx]
+
+    str_idx = 1
+    while str_idx < strs.length
+      return idx > 0 ? strs[0][0..idx-1] : '' if strs[str_idx].length <= idx
+
+      return '' if strs[str_idx][idx] != cur_char && idx.zero?
+      return strs[0][0..idx - 1] if strs[str_idx][idx] != cur_char
+      str_idx += 1
+    end
+
+    idx += 1
+  end
+
+  idx > 0 ? strs[0][0..idx] : ''
+end