[juhui-jeong] WEEK 14 Solutions

binary-tree-level-order-traversal/juhui-jeong.java

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+// BFS 구현
+// null 처리 잘 확인할 것...
+class Solution {
+    public List<List<Integer>> levelOrder(TreeNode root) {
+        List<List<Integer>> result = new ArrayList<>();
+        if (root == null) return result;
+
+        Queue<TreeNode> queue = new LinkedList<>();
+        queue.offer(root);
+
+        while(!queue.isEmpty()) {
+            int size = queue.size();
+            List<Integer> level = new ArrayList<>();
+
+            for (int i = 0; i < size; i++) {
+                TreeNode cur = queue.poll();
+                level.add(cur.val);
+
+                if (cur.left != null) queue.offer(cur.left);
+                if (cur.right != null) queue.offer(cur.right);
+            }
+            result.add(level);
+        }
+        return result;
+    }
+}

counting-bits/juhui-jeong.java

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+
+
+class Solution {
+    public int[] countBits(int n) {
+        ArrayList<Integer> list = new ArrayList<>();
+
+        for (int i = 0; i <= n; i++) {
+            int result = i;
+            int cnt = 0;
+
+            while(result > 0) {
+                cnt += result%2;
+                result /= 2;
+            }
+
+            list.add(cnt);
+        }
+        int[] ans = new int[list.size()];
+        for (int i = 0; i < list.size(); i++) {
+            ans[i] = list.get(i);
+        }
+        return ans;
+    }
+}

house-robber-ii/juhui-jeong.java

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+class Solution {
+    public int rob(int[] nums) {
+        int n = nums.length;
+        if (n == 1) return nums[0];
+        if (n == 2) return Math.max(nums[0], nums[1]);
+
+        return Math.max(robRange(nums, 0, n - 2), robRange(nums, 1, n - 1));
+    }
+
+    private int robRange(int[] nums, int start, int end) {
+        int prev2 = 0;
+        int prev1 = 0;
+
+        for (int i = start; i <= end; i++) {
+            int cur = Math.max(prev1, prev2 + nums[i]);
+            prev2 = prev1;
+            prev1 = cur;
+        }
+        return prev1;
+    }
+}