LeetCode in Kotlin

1519. Number of Nodes in the Sub-Tree With the Same Label

Medium

You are given a tree (i.e. a connected, undirected graph that has no cycles) consisting of n nodes numbered from 0 to n - 1 and exactly n - 1 edges. The root of the tree is the node 0, and each node of the tree has a label which is a lower-case character given in the string labels (i.e. The node with the number i has the label labels[i]).

The edges array is given on the form edges[i] = [a_i, b_i], which means there is an edge between nodes a_i and b_i in the tree.

Return an array of size n where ans[i] is the number of nodes in the subtree of the i^th node which have the same label as node i.

A subtree of a tree T is the tree consisting of a node in T and all of its descendant nodes.

Example 1:

Input: n = 7, edges = [[0,1],[0,2],[1,4],[1,5],[2,3],[2,6]], labels = “abaedcd”

Output: [2,1,1,1,1,1,1]

Explanation: Node 0 has label ‘a’ and its sub-tree has node 2 with label ‘a’ as well, thus the answer is 2. Notice that any node is part of its sub-tree.

Node 1 has a label ‘b’. The sub-tree of node 1 contains nodes 1,4 and 5, as nodes 4 and 5 have different labels than node 1, the answer is just 1 (the node itself).

Example 2:

Input: n = 4, edges = [[0,1],[1,2],[0,3]], labels = “bbbb”

Output: [4,2,1,1]

Explanation: The sub-tree of node 2 contains only node 2, so the answer is 1.

The sub-tree of node 3 contains only node 3, so the answer is 1.

The sub-tree of node 1 contains nodes 1 and 2, both have label ‘b’, thus the answer is 2.

The sub-tree of node 0 contains nodes 0, 1, 2 and 3, all with label ‘b’, thus the answer is 4.

Example 3:

Input: n = 5, edges = [[0,1],[0,2],[1,3],[0,4]], labels = “aabab”

Output: [3,2,1,1,1]

Constraints:

1 <= n <= 10⁵
edges.length == n - 1
edges[i].length == 2
0 <= a_i, b_i < n
a_i != b_i
labels.length == n
labels is consisting of only of lowercase English letters.

Solution

class Solution {
    fun countSubTrees(n: Int, edges: Array<IntArray>, labelsString: String): IntArray {
        val labelsCount = IntArray(n)
        if (n <= 0) {
            return labelsCount
        }
        val labels = IntArray(n)
        var nodeNumber = 0
        for (label in labelsString.toCharArray()) {
            labels[nodeNumber++] = label.code - 'a'.code
        }
        val graph = ArrayList<ArrayList<Int>>()
        for (i in 0 until n) {
            graph.add(ArrayList())
        }
        for (edge in edges) {
            val parent = edge[0]
            val child = edge[1]
            graph[parent].add(child)
            graph[child].add(parent)
        }
        getLabelsFrequency(0, graph, labels, labelsCount, 0)
        return labelsCount
    }

    private fun getLabelsFrequency(
        root: Int,
        graph: ArrayList<ArrayList<Int>>,
        labels: IntArray,
        labelsCount: IntArray,
        parent: Int
    ): IntArray {
        val labelsFrequency = IntArray(26)
        val rootLabel = labels[root]
        labelsFrequency[rootLabel]++
        for (child in graph[root]) {
            if (child == parent) {
                continue
            }
            val childLabelsFrequency = getLabelsFrequency(child, graph, labels, labelsCount, root)
            for (i in childLabelsFrequency.indices) {
                labelsFrequency[i] += childLabelsFrequency[i]
            }
        }
        labelsCount[root] = labelsFrequency[rootLabel]
        return labelsFrequency
    }
}

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