_111.java

package com.fishercoder.solutions;

import com.fishercoder.common.classes.TreeNode;

import java.util.LinkedList;
import java.util.Queue;

/**
 * 111. Minimum Depth of Binary Tree
 *
 * 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.
 * */

public class _111 {
    public static class Solution1 {
      /**DFS*/
      public int minDepth(TreeNode root) {
        if (root == null) {
          return 0;
        }
        int left = minDepth(root.left);
        int right = minDepth(root.right);
        if (left == 0) {
          return right + 1;
        }
        if (right == 0) {
          return left + 1;
        }
        return Math.min(left, right) + 1;
      }
    }

  public static class Solution2 {
    /**BFS*/
    public int minDepth(TreeNode root) {
      if (root == null) {
        return 0;
      }
      Queue<TreeNode> q = new LinkedList();
      q.offer(root);
      int level = 0;
      while (!q.isEmpty()) {
        level++;
        int size = q.size();
        for (int i = 0; i < size; i++) {
          TreeNode curr = q.poll();
          if (curr.left != null) {
            q.offer(curr.left);
          }
          if (curr.right != null) {
            q.offer(curr.right);
          }
          if (curr.left == null && curr.right == null) {
            return level;
          }
        }
      }
      return level;
    }
  }
}