@@ -741,6 +741,99 @@ impl Solution{
741741 }
742742}
743743```
744+ ### C#
745+ ``` C#
746+ // 前序遍历
747+ public IList < int > PreorderTraversal (TreeNode root )
748+ {
749+ var res = new List <int >();
750+ var st = new Stack <TreeNode >();
751+ if (root == null ) return res ;
752+ st .Push (root );
753+ while (st .Count != 0 )
754+ {
755+ var node = st .Peek ();
756+ if (node == null )
757+ {
758+ st .Pop ();
759+ node = st .Peek ();
760+ st .Pop ();
761+ res .Add (node .val );
762+ }
763+ else
764+ {
765+ st .Pop ();
766+ if (node .right != null ) st .Push (node .right );
767+ if (node .left != null ) st .Push (node .left );
768+ st .Push (node );
769+ st .Push (null );
770+ }
771+ }
772+ return res ;
773+ }
774+ ```
775+ ``` C#
776+ // 中序遍历
777+ public IList < int > InorderTraversal (TreeNode root )
778+ {
779+ var res = new List <int >();
780+ var st = new Stack <TreeNode >();
781+ if (root == null ) return res ;
782+ st .Push (root );
783+ while (st .Count != 0 )
784+ {
785+ var node = st .Peek ();
786+ if (node == null )
787+ {
788+ st .Pop ();
789+ node = st .Peek ();
790+ st .Pop ();
791+ res .Add (node .val );
792+ }
793+ else
794+ {
795+ st .Pop ();
796+ if (node .right != null ) st .Push (node .right );
797+ st .Push (node );
798+ st .Push (null );
799+ if (node .left != null ) st .Push (node .left );
800+ }
801+ }
802+ return res ;
803+ }
804+ ```
805+ 806+ ``` C#
807+ // 后序遍历
808+ public IList < int > PostorderTraversal (TreeNode root )
809+ {
810+ var res = new List <int >();
811+ var st = new Stack <TreeNode >();
812+ if (root == null ) return res ;
813+ st .Push (root );
814+ while (st .Count != 0 )
815+ {
816+ var node = st .Peek ();
817+ if (node == null )
818+ {
819+ st .Pop ();
820+ node = st .Peek ();
821+ st .Pop ();
822+ res .Add (node .val );
823+ }
824+ else
825+ {
826+ st .Pop ();
827+ if (node .left != null ) st .Push (node .left );
828+ if (node .right != null ) st .Push (node .right );
829+ st .Push (node );
830+ st .Push (null );
831+ }
832+ }
833+ res .Reverse (0 , res .Count );
834+ return res ;
835+ }
836+ ```
744837
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