[JeonJe] WEEK 08 Solutions

clone-graph/JeonJe.java

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+import java.util.*;
+
+// TC: O(V + E)
+// SC: O(V)
+class Solution {
+    public Node cloneGraph(Node node) {
+        return deepCopy(node, new HashMap<>());
+    }
+
+    private Node deepCopy(Node node, Map<Node, Node> cloned) {
+        if (node == null) {
+            return null;
+        }
+
+        if (cloned.containsKey(node)) {
+            return cloned.get(node);
+        }
+
+        Node clonedNode = new Node(node.val);
+        cloned.put(node, clonedNode);
+
+        for (Node neighbor : node.neighbors) {
+            clonedNode.neighbors.add(deepCopy(neighbor, cloned));
+        }
+
+        return clonedNode;
+    }
+}

longest-common-subsequence/JeonJe.java

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+// TC: O(m * n)
+// SC: O(m * n)
+class Solution {
+
+    public int longestCommonSubsequence(String text1, String text2) {
+        int[][] dp = new int[text1.length() + 1][text2.length() + 1];
+
+        for (int i = text1.length() - 1; i >= 0; i--) {
+            for (int j = text2.length() - 1; j >= 0; j--) {
+
+                dp[i][j] = text1.charAt(i) == text2.charAt(j) ?
+                        1 + dp[i + 1][j + 1] :
+                        Math.max(dp[i + 1][j], dp[i][j + 1]);
+
+            }
+        }
+        return dp[0][0];
+    }
+
+}

longest-repeating-character-replacement/JeonJe.java

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+import java.util.*;
+
+// TC: O(n)
+// SC: O(1)
+class Solution {
+    public int characterReplacement(String s, int k) {
+        int[] counts = new int[26];
+        int left = 0;
+
+        for (int right = 0; right < s.length(); right++) {
+            counts[toAlphabetIndex(s.charAt(right))]++;
+
+            int windowLength = right - left + 1;
+            int mostFreq = Arrays.stream(counts).max().getAsInt();
+            //바꿀 대상이 k 횟수보다 크면, left을 옮김
+            if (windowLength - mostFreq > k) {
+                counts[toAlphabetIndex(s.charAt(left))]--;
+                left++;
+            }
+        }
+
+        return s.length() - left;
+    }
+
+    private int toAlphabetIndex(char c) {
+        return c - 'A';
+    }
+
+}

reverse-bits/JeonJe.java

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+import java.util.*;
+
+// TC: O(1)
+// SC: O(1)
+class Solution {
+    public int reverseBits(int n) {
+        int answer = 0;
+        for (int i = 0; i < 32; i++) {
+            int bitFlag = (n >> i) & 1;
+            answer += (bitFlag << (31 - i));
+        }
+        return answer;
+    }
+}