Merge pull request illuz#2 from NgWilli/patch-2

bug fix #018 4sum

Author: illuz

solutions/018.4Sum/AC_two_points_n3.cpp

@@ -40,10 +40,10 @@ class Solution {
                             --k;
                     }
                 }
-                while (m < len && num[m] == num[m + 1])
+                while (m < len-3 && num[m] == num[m + 1])
                     ++m;
             }
-            while (i < len && num[i] == num[i + 1])
+            while (i < len-4 && num[i] == num[i + 1])
                 ++i;
         }