LeetCode 1519: Number of Nodes in the Sub-Tree With the Same Label Solution

class Solution {
    public int[] countSubTrees(int n, int[][] edges, String labels) {
        Map<Integer, List<Integer>> graph = new HashMap<>();
        for (int[] edge : edges) {
            graph.computeIfAbsent(edge[0], k -> new ArrayList<>()).add(edge[1]);
            graph.computeIfAbsent(edge[1], k -> new ArrayList<>()).add(edge[0]);
        }

        int[] ans = new int[n];
        int[] count = new int[26]; // Count of each label in the subtree of a node
        boolean[] visited = new boolean[n];

        dfs(0, graph, labels, count, visited, ans);

        return ans;
    }

    private void dfs(int node, Map<Integer, List<Integer>> graph, String labels, int[] count, boolean[] visited, int[] ans) {
        visited[node] = true;
        int label = labels.charAt(node) - 'a';

        int[] temp = new int[26];
        temp[label] = 1;

        for (int child : graph.getOrDefault(node, new ArrayList<>())) {
            if (!visited[child]) {
                int[] childCount = new int[26];
                dfs(child, graph, labels, childCount, visited, ans);
                for (int i = 0; i < 26; i++) {
                    temp[i] += childCount[i];
                }
            }
        }

        ans[node] = temp[label];
        count[label] += temp[label];
        for (int i = 0; i < 26; i++) {
            ans[node] -= Math.min(count[i], temp[i]);
        }
    }
}