go: add «951. Flip Equivalent Binary Trees»

URL:	https://leetcode.com/problems/flip-equivalent-binary-trees/
Signed-off-by: Matej Focko <me@mfocko.xyz>

go/flip-equivalent-binary-trees.go

@@ -0,0 +1,26 @@
+package main
+
+func flipEquiv(left, right *TreeNode) bool {
+	// reached leaves
+	if left == nil && right == nil {
+		return true
+	}
+
+	// reached only one leaf
+	if left == nil || right == nil {
+		return false
+	}
+
+	// can't build equivalent subtrees
+	if left.Val != right.Val {
+		return false
+	}
+
+	// no swap
+	isEquiv := flipEquiv(left.Left, right.Left) && flipEquiv(left.Right, right.Right)
+
+	// with swap
+	isEquiv = isEquiv || (flipEquiv(left.Left, right.Right) && flipEquiv(left.Right, right.Left))
+
+	return isEquiv
+}