cs: add “872. Leaf-Similar Trees”

Signed-off-by: Matej Focko <mfocko@redhat.com>

cs/leaf-similar-trees.cs

@@ -0,0 +1,52 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     public int val;
+ *     public TreeNode left;
+ *     public TreeNode right;
+ *     public TreeNode(int val=0, TreeNode left=null, TreeNode right=null) {
+ *         this.val = val;
+ *         this.left = left;
+ *         this.right = right;
+ *     }
+ * }
+ */
+public class Solution {
+    private static IEnumerable<int> Leafs(TreeNode node) {
+        if (node == null) {
+            yield break;
+        }
+
+        var stack = new Stack<TreeNode>();
+        stack.Push(node);
+
+        while (stack.Count > 0) {
+            var n = stack.Pop();
+
+            if (n.left == null && n.right == null) {
+                yield return n.val;
+            }
+
+            if (n.right != null) {
+                stack.Push(n.right);
+            }
+            if (n.left != null) {
+                stack.Push(n.left);
+            }
+        }
+    }
+
+    public bool LeafSimilar(TreeNode root1, TreeNode root2) {
+        var xs = Leafs(root1).GetEnumerator();
+        var ys = Leafs(root2).GetEnumerator();
+
+        bool hasX = xs.MoveNext(), hasY = ys.MoveNext();
+        for (; hasX && hasY; hasX = xs.MoveNext(), hasY = ys.MoveNext()) {
+            if (xs.Current != ys.Current) {
+                return false;
+            }
+        }
+
+        return hasX == hasY;
+    }
+}