Given a tree with n nodes. Each node has k coins, where 0 <= k <= n . There are total n coins on the tree.
The goal is to move the coins such that each node has exactly one coin. What's the minimum moves required?
Each move can only move one coin to an adjacent node.

    int moveCoins(TreeNode root) {
        return dfs(root, new HashMap<>());
    }

    int dfs(TreeNode n, Map count) {
        if(!count.containsKey(n)) {
            count.put(n, n.val);
        }
        int coinsNum = count.get(n);
        int res = 0;
        for(TreeNode kid : n.children) {
            res += dfs(kid, count);
            coinsNum += count.get(kid);
            res += Math.abs(count.get(kid));
        }
        count.put(n, coinsNum - 1);
        return res;
    }