[eunhwa99] week 1

contains-duplicate/eunhwa99.java

@@ -0,0 +1,14 @@
+class Solution {
+    public boolean containsDuplicate(int[] nums) {
+         HashSet<Integer> seen = new HashSet<>();
+        for (int num : nums) {
+            if (!seen.add(num)) {
+                return true;
+            }
+        }
+
+        return false;
+
+
+    }
+}

house-robber/eunhwa99.java

@@ -0,0 +1,24 @@
+import java.util.Arrays;
+
+class Solution {
+    int size = 0;
+    int[] numArray;
+    int[] dp;
+
+    public int rob(int[] nums) {
+        size = nums.length;
+        dp = new int[size];
+        // 배열의 모든 값을 -1로 변경
+        Arrays.fill(dp, -1);
+        numArray = nums;
+        return fun(0);
+    }
+
+    private int fun(int idx) {
+        if (idx >= size) return 0;
+        if (dp[idx] != -1) return dp[idx];
+        dp[idx] = 0; // check
+        dp[idx] += Math.max(fun(idx + 2) + numArray[idx], fun(idx + 1));
+        return dp[idx];
+    }
+}

longest-consecutive-sequence/eunhwa99.java

@@ -0,0 +1,23 @@
+import java.util.HashSet;
+
+class Solution {
+    public int longestConsecutive(int[] nums) {
+        HashSet<Integer> mySet = new HashSet<Integer>();
+
+        for (int num : nums) {
+            mySet.add(num);
+        }
+
+        int result = 0;
+        for (int num : mySet) {
+            int cnt = 1;
+            if (!mySet.contains(num - 1)) {
+                while (mySet.contains(++num)) {
+                    ++cnt;
+                }
+                result = Math.max(cnt, result);
+            }
+        }
+        return result;
+    }
+}

top-k-frequent-elements/eunhwa99.java

@@ -0,0 +1,16 @@
+import java.util.HashMap;
+import java.util.Map;
+class Solution {
+    public static int[] topKFrequent(int[] nums, int k) {
+        Map<Integer, Integer> myMap = new HashMap<>();
+        for (int num : nums) {
+            myMap.put(num, myMap.getOrDefault(num, 0) + 1);
+        }
+        return myMap.entrySet()
+                .stream()
+                .sorted((v1, v2) -> Integer.compare(v2.getValue(),v1.getValue()))
+                .map(Map.Entry::getKey)
+                .mapToInt(Integer::intValue)
+                .toArray();
+    }
+}

valid-palindrome/eunhwa99.java

@@ -0,0 +1,23 @@
+class Solution {
+    public boolean isPalindrome(String s) {
+        StringBuilder str = new StringBuilder();
+
+        for (int i = 0; i < s.length(); i++) {
+            char c = s.charAt(i);
+            if (Character.isLetterOrDigit(c)) {
+                str.append(Character.toLowerCase(c));  
+            }
+        }
+
+        int left = 0, right = str.length() - 1;
+        while (left < right) {
+            if (str.charAt(left) != str.charAt(right)) {
+                return false;  
+            }
+            left++;
+            right--;
+        }
+
+        return true;  
+    }
+}