public class Solution {
    private int GetSwaps(int[] level) {
        int[] sorted = (int[])level.Clone();
        Array.Sort(sorted);

        var indices = new Dictionary<int, int>();
        for (int i = 0; i < level.Length; ++i) {
            indices[level[i]] = i;
        }

        var swaps = 0;
        for (int i = 0; i < level.Length; ++i) {
            if (level[i] == sorted[i]) {
                continue;
            }

            ++swaps;
            var current = indices[sorted[i]];
            indices[level[i]] = current;
            level[current] = level[i];
        }

        return swaps;
    }

    public int MinimumOperations(TreeNode root) {
        var q = new Queue<TreeNode>();
        q.Enqueue(root);

        var swaps = 0;
        while (q.Count > 0) {
            var size = q.Count;

            var level = new int[size];
            for (int i = 0; i < size; ++i) {
                var node = q.Dequeue();
                level[i] = node.val;

                foreach (var n in new TreeNode[] { node.left, node.right }) {
                    if (n != null) {
                        q.Enqueue(n);
                    }
                }
            }

            swaps += GetSwaps(level);
        }

        return swaps;
    }
}