Minimum Height Trees LeetCode Solution

Here, We see Minimum Height Trees LeetCode Solution. This Leetcode problem is done in many programming languages like C++, Java, JavaScript, Python, etc. with different approaches.

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Minimum Height Trees LeetCode Solution

Minimum Height Trees LeetCode Solution

Problem Statement

A tree is an undirected graph in which any two vertices are connected by exactly one path. In other words, any connected graph without simple cycles is a tree.

Given a tree of n nodes labelled from 0 to n – 1, and an array of n – 1 edges where edges[i] = [ai, bi] indicates that there is an undirected edge between the two nodes ai and bi in the tree, you can choose any node of the tree as the root. When you select a node x as the root, the result tree has height h. Among all possible rooted trees, those with minimum height (i.e. min(h))  are called minimum height trees (MHTs).

Return a list of all MHTs’ root labels. You can return the answer in any order.

The height of a rooted tree is the number of edges on the longest downward path between the root and a leaf.

Example 1:

e1

Input: n = 4, edges = [[1,0],[1,2],[1,3]]
Output: [1]
Explanation: As shown, the height of the tree is 1 when the root is the node with label 1 which is the only MHT.

Example 2:

e2

Input: n = 6, edges = [[3,0],[3,1],[3,2],[3,4],[5,4]]
Output: [3,4]

Minimum Height Trees LeetCode Solution C++

class Solution {
public:
    vector<int> findMinHeightTrees(int n, vector<vector<int>>& edges) {
        vector<vector<int>> graph(n);
        vector<int> indegree(n, 0), ans;
        for(auto &e : edges){
            graph[e[0]].push_back(e[1]);
            graph[e[1]].push_back(e[0]);
            indegree[e[0]]++;
            indegree[e[1]]++;
        }
        queue<int> q;
        for(int i=0; i<n;i++){
            if(indegree[i]==1) q.push(i), indegree[i]--;
        } 
        while(!q.empty()){
            int s = q.size();
            ans.clear();
            for(int i=0; i<s;i++){
                int curr = q.front(); q.pop();
                ans.push_back(curr);
                for(auto child : graph[curr]){
                    indegree[child]--;
                    if(indegree[child]==1) q.push(child);   
                }
            }
        }
        if(n==1) ans.push_back(0);
        return ans;
    }
};Code language: PHP (php)

Minimum Height Trees LeetCode Solution Java

class Solution {
    public List<Integer> findMinHeightTrees(int n, int[][] edges) {
        if (n == 1) return Collections.singletonList(0);
        List<Set<Integer>> adj = new ArrayList<>(n);
        for (int i = 0; i < n; ++i) adj.add(new HashSet<>());
        for (int[] edge : edges) {
            adj.get(edge[0]).add(edge[1]);
            adj.get(edge[1]).add(edge[0]);
        }
        List<Integer> leaves = new ArrayList<>();
        for (int i = 0; i < n; ++i)
            if (adj.get(i).size() == 1) leaves.add(i);
        while (n > 2) {
            n -= leaves.size();
            List<Integer> newLeaves = new ArrayList<>();
            for (int i : leaves) {
                int j = adj.get(i).iterator().next();
                adj.get(j).remove(i);
                if (adj.get(j).size() == 1) newLeaves.add(j);
            }
            leaves = newLeaves;
        }
        return leaves;
    }
}Code language: PHP (php)

Minimum Height Trees Solution JavaScript

var findMinHeightTrees = function(n, edges) {
    if (!edges || n < 2) return [0];
    let graph = [];
    for (let [x, y] of edges) {
        graph[x] = graph[x] || [];
        graph[y] = graph[y] || [];
        graph[x].push(y);
        graph[y].push(x);
    }
    let leaves = [];
    graph.map((pts,i) => pts.length === 1 && leaves.push(i));
    while (n > 2) {
        n = n - leaves.length;
        let nxt_leaves = [];
        for (let leave of leaves) {
            tmp = graph[leave].pop();
            graph[tmp].splice(graph[tmp].indexOf(leave),1);
            graph[tmp].length === 1 && nxt_leaves.push(tmp);
        }
        leaves = nxt_leaves;
    }
    return leaves;
};Code language: JavaScript (javascript)

Minimum Height Trees Solution Python

class Solution(object):
    def findMinHeightTrees(self, n, edges):
        if n == 1: return [0] 
        adj = [set() for _ in xrange(n)]
        for i, j in edges:
            adj[i].add(j)
            adj[j].add(i)
        leaves = [i for i in xrange(n) if len(adj[i]) == 1]
        while n > 2:
            n -= len(leaves)
            newLeaves = []
            for i in leaves:
                j = adj[i].pop()
                adj[j].remove(i)
                if len(adj[j]) == 1: newLeaves.append(j)
            leaves = newLeaves
        return leaves
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