@@ -897,6 +897,53 @@ impl Solution {
897897 }
898898}
899899```
900+ ### C#
901+ ``` C#
902+ // 递归
903+ public bool IsSymmetric (TreeNode root )
904+ {
905+ if (root == null ) return true ;
906+ return Compare (root .left , root .right );
907+ }
908+ public bool Compare (TreeNode left , TreeNode right )
909+ {
910+ if (left == null && right != null ) return false ;
911+ else if (left != null && right == null ) return false ;
912+ else if (left == null && right == null ) return true ;
913+ else if (left .val != right .val ) return false ;
914+ 915+ var outside = Compare (left .left , right .right );
916+ var inside = Compare (left .right , right .left );
917+ 918+ return outside && inside ;
919+ }
920+ ```
921+ ``` C#
922+ // 迭代法
923+ public bool IsSymmetric (TreeNode root )
924+ {
925+ if (root == null ) return true ;
926+ var st = new Stack <TreeNode >();
927+ st .Push (root .left );
928+ st .Push (root .right );
929+ while (st .Count != 0 )
930+ {
931+ var left = st .Pop ();
932+ var right = st .Pop ();
933+ if (left == null && right == null )
934+ continue ;
935+ 936+ if ((left == null || right == null || (left .val != right .val )))
937+ return false ;
938+ 939+ st .Push (left .left );
940+ st .Push (right .right );
941+ st .Push (left .right );
942+ st .Push (right .left );
943+ }
944+ return true ;
945+ }
946+ ```
900947
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