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Minimum Depth of Binary Tree

Problem Description​

Given a binary tree, find its minimum depth.

The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.

Examples​

Example 1:

LeetCode Problem - Binary Tree

Input: root = [3,9,20,null,null,15,7]
Output: 2

Constraints​

  • The number of nodes in the tree is in the range [0, 105].
  • −100<=Node.val<=100-100 <= Node.val <= 100

Solution for Binary Tree Problem​

Intuition And Approach​

To find the minimum depth of a binary tree, we can perform a depth-first search (DFS) or a breadth-first search (BFS). Here, we will use BFS for simplicity.

Breadth-First Search (BFS): Traverse the tree level by level, stopping as soon as we encounter a leaf node. The depth of the first leaf node encountered will be the minimum depth of the tree.

Code in Different Languages​

Written by @Vipullakum007
class Solution {
public int minDepth(TreeNode root) {
if (root == null) return 0;
Queue<TreeNode> queue = new LinkedList<>();
queue.offer(root);
int depth = 1;
while (!queue.isEmpty()) {
int levelSize = queue.size();
for (int i = 0; i < levelSize; i++) {
TreeNode node = queue.poll();
if (node.left == null && node.right == null) return depth;
if (node.left != null) queue.offer(node.left);
if (node.right != null) queue.offer(node.right);
}
depth++;
}
return depth;
}
}

Complexity Analysis​

  • Time Complexity: O(n)O(n) where n is the number of nodes in the binary tree.
  • Space Complexity: O(h)O(h) where h is the height of the binary tree.