[sm9171] Week01 Solutions

contains-duplicate/sm9171.java

@@ -0,0 +1,13 @@
+class Solution {
+    public boolean containsDuplicate(int[] nums) {
+        HashSet<Integer> set = new HashSet<>();
+
+        for (int i = 0; i < nums.length; i++) {
+            if (set.contains(nums[i])) {
+                return true;
+            }
+            set.add(nums[i]);
+        }
+        return false;
+    }
+}

house-robber/sm9171.java

@@ -0,0 +1,14 @@
+class Solution {
+    public int rob(int[] nums) {
+        if (nums.length == 0) return 0;
+        if (nums.length == 1) return nums[0];
+
+        nums[1] = Math.max(nums[0], nums[1]);
+
+        for (int i = 2; i < nums.length; i++) {
+            nums[i] = Math.max(nums[i - 1], nums[i - 2] + nums[i]);
+        }
+
+        return nums[nums.length - 1];
+    }
+}

longest-consecutive-sequence/sm9171.java

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+class Solution {
+    public int longestConsecutive(int[] nums) {
+        int longest = 0;
+        Set<Integer> set = Arrays.stream(nums)
+                .boxed()
+                .collect(Collectors.toSet());
+
+        for (Integer i : set) {
+            if (set.contains(i - 1)) continue;
+            int length = 1;
+
+            while (set.contains(i + 1)) {
+                length++;
+                i++;
+            }
+            longest = Math.max(longest, length);
+        }
+        return longest;
+    }
+}

top-k-frequent-elements/sm9171.java

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+class Solution {
+    public static int[] topKFrequent(int[] nums, int k) {
+        Map<Integer, Integer> hashMap = new HashMap<>();
+        for (int i = 0; i < nums.length; i++) {
+            int num = nums[i];
+            hashMap.put(num, hashMap.getOrDefault(num, 0) + 1);
+        }
+
+        List<Integer> list = hashMap.entrySet().stream()
+                .sorted(Map.Entry.<Integer, Integer>comparingByValue().reversed())
+                .limit(k)
+                .map(Map.Entry::getKey)
+                .toList();
+
+        int[] result = list.stream()
+                .mapToInt(Integer::intValue)
+                .toArray();
+
+        return result;
+    }
+}

two-sum/sm9171.java

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+class Solution {
+    public int[] twoSum(int[] nums, int target) {
+        Map<Integer, Integer> hashMap = new HashMap<>();
+
+        for (int i = 0; i < nums.length; i++) {
+            int gap = target - nums[i];
+            if(hashMap.containsKey(gap)){
+                int j = hashMap.get(gap);
+                return new int[]{i,j};
+            }
+            hashMap.put(nums[i], i);
+        }
+        return null;
+    }
+}