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Author: shimhun99

LeetCode/Easy/0111-minimum-depth-of-binary-tree/0111-minimum-depth-of-binary-tree.java

@@ -1,25 +1,54 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode() {}
+ *     TreeNode(int val) { this.val = val; }
+ *     TreeNode(int val, TreeNode left, TreeNode right) {
+ *         this.val = val;
+ *         this.left = left;
+ *         this.right = right;
+ *     }
+ * }
+ */
+import java.util.*;
+
 class Solution {
+    Queue<TreeNode> queue = new ArrayDeque<>();
+
     public int minDepth(TreeNode root) {
-        if (root == null) return 0;
+        // //dfs
+        // if(root == null) return 0;
+        // int left = minDepth(root.left);
+        // int right = minDepth(root.right);
+
+        // //한쪽 자식이 0이면 null이므로 값이 없다는 소리이므로 반대편 리프노드 값으로 계산
+        // if(left==0 || right==0) return Math.max(left,right)+1;
+        
+        // //왼쪽, 오른쪽 자식 모두 값이 있다면, 최솟값으로 계산
+        // return Math.min(left,right)+1;
+
+        //bfs
+        if(root == null) return 0;
 
-        Queue<TreeNode> queue = new LinkedList<>();
-        queue.offer(root);
-        int depth = 1;
+        queue.add(root);
+        int minDepth = 0;
 
-        while (!queue.isEmpty()) {
-            int levelSize = queue.size();
+        while(!queue.isEmpty()){
+            int queueLen = queue.size();
 
-            for (int i = 0; i < levelSize; i++) {
+            while(queueLen-->0){
                 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);
+                if(node.left==null && node.right==null) return minDepth;
+                if(node.left!=null) queue.add(node.left);
+                if(node.right!=null) queue.add(node.right);
             }
 
-            depth++;
-        }
+            minDepth++;
+        }  
 
-        return depth;
+        return minDepth;
     }
 }