Longest substrings without repeating characters: Difference between revisions

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 Input: ""
 Result: []
+</pre>
+=={{header|Ada}}==
+<lang Ada>with Ada.Text_IO;
+procedure Longest_Substring is
+   function Longest (Item : String) return String is
+      Hist  : array (Character) of Natural := (others => 0);
+      First         : Natural := Item'First;
+      Last          : Natural := Item'First - 1;
+      Longest_First : Natural := Item'First;
+      Longest_Last  : Natural := Item'First - 1;
+      procedure Adjust is
+      begin
+         if Last - First > Longest_Last - Longest_First then
+            Longest_First := First;
+            Longest_Last  := Last;
+         end if;
+      end Adjust;
+   begin
+      if Item = "" then
+         return Item;
+      end if;
+      for Index in Item'Range loop
+         Last := Index;
+         Hist (Item (Index)) := Hist (Item (Index)) + 1;
+         if Hist (Item (Index)) = 1 then
+            Adjust;
+         else
+            for A in First .. Index loop
+               if (for all E of Hist => E <= 1) then
+                  First := A;
+                  Adjust;
+                  exit;
+               end if;
+               Hist (Item (A)) := Hist (Item (A)) - 1;
+            end loop;
+         end if;
+      end loop;
+      return Item (Longest_First .. Longest_Last);
+   end Longest;
+   procedure Test (Item : String) is
+      use Ada.Text_IO;
+   begin
+      Put ("original : '");  Put (Item);            Put_Line ("'");
+      Put ("longest  : '");  Put (Longest (Item));  Put_Line ("'");
+   end Test;
+begin
+   Test ("");
+   Test ("a");
+   Test ("xyzyabcybdfd");
+   Test ("thisisastringtest");
+   Test ("zzzzz");
+end Longest_Substring;</lang>
+{{out}}
+<pre>
+original : ''
+longest  : ''
+original : 'a'
+longest  : 'a'
+original : 'xyzyabcybdfd'
+longest  : 'zyabc'
+original : 'thisisastringtest'
+longest  : 'astring'
+original : 'zzzzz'
+longest  : 'z'
 </pre>