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# Minimum Height Trees LeetCode Solution

## Problem – Minimum Height Trees LeetCode Solution

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

Constraints:

• `1 <= n <= 2 * 104`
• `edges.length == n - 1`
• `0 <= ai, bi < n`
• `ai != bi`
• All the pairs `(ai, bi)` are distinct.
• The given input is guaranteed to be a tree and there will be no repeated edges.

## Minimum Height Trees LeetCode Solution in Java

``````public List<Integer> findMinHeightTrees(int n, int[][] edges) {
if (n == 1) return Collections.singletonList(0);

for (int[] edge : edges) {
}

List<Integer> leaves = new ArrayList<>();
for (int i = 0; i < n; ++i)

while (n > 2) {
n -= leaves.size();
List<Integer> newLeaves = new ArrayList<>();
for (int i : leaves) {
}
leaves = newLeaves;
}
return leaves;
}

``````

## Minimum Height Trees LeetCode Solution in Python

``````def findMinHeightTrees(self, n, edges):
if n == 1: return 
adj = [set() for _ in xrange(n)]
for i, j in edges:

leaves = [i for i in xrange(n) if len(adj[i]) == 1]

while n > 2:
n -= len(leaves)
newLeaves = []
for i in leaves:
leaves = newLeaves
return leaves
``````

## Minimum Height Trees LeetCode Solution in C++

``````class Solution {
public:
vector<int> findMinHeightTrees(int n, vector<vector<int>>& edges) {
if(n==0)
return {};
if(n==1)
return {0};
vector<int>res;
vector<int>degrees(n,0);
for(int i=0;i<edges.size();i++)
{
degrees[edges[i]]++;//updating how many edges each node has
degrees[edges[i]]++;
}
queue<int>queue;
for(int i=0;i<n;i++)
{
queue.push(i);
}
while(!queue.empty())
{
res.clear();// clear vector before we start traversing level by level.
int size=queue.size();
for(int i=0;i<size;i++)
{
int cur=queue.front();
queue.pop();
res.push_back(cur);//adding nodes to vector.Goal is to get a vector of  just 1 or 2 nodes available.
{
degrees[neighbor]--;//removing current leave nodes
queue.push(neighbor);
}
}
}
return res;
}
};
``````
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