[sm9171] Week01 Solutions

contains-duplicate/sm9171.java

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

top-k-frequent-elements/sm9171.java

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