[xeulbn] WEEK 01 solutions

contains-duplicate/xeulbn.java

@@ -0,0 +1,15 @@
+import java.util.*;
+
+class Solution {
+    public boolean containsDuplicate(int[] nums) {
+        Set<Integer> numberCheck = new HashSet<>();
+
+        for(int num : nums){
+            if(numberCheck.contains(num)){
+                return true;
+            }
+            numberCheck.add(num);
+        }
+        return false;
+    }
+}

house-robber/xeulbn.java

@@ -0,0 +1,21 @@
+import java.util.*;
+
+class Solution {
+
+    public int rob(int[] nums) {
+        if (nums.length == 1) {
+            return nums[0];
+        }
+
+        int[] dp = new int[nums.length];
+
+        dp[0] = nums[0];
+        dp[1] = Math.max(nums[0], nums[1]);
+
+        for (int i = 2; i < nums.length; i++) {
+            dp[i] = Math.max(dp[i - 1], dp[i - 2] + nums[i]);
+        }
+
+        return dp[nums.length - 1];
+    }
+}

longest-consecutive-sequence/xeulbn.java

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+import java.util.*;
+
+class Solution {
+    public int longestConsecutive(int[] nums) {
+        Set<Integer> set = new HashSet<>();
+
+        for (int num : nums) {
+            set.add(num);
+        }
+
+        int maxLength = 0;
+
+        for (int num : set) {
+            if (!set.contains(num - 1)) {
+                int currentNum = num;
+                int currentLength = 1;
+
+                while (set.contains(currentNum + 1)) {
+                    currentNum++;
+                    currentLength++;
+                }
+
+                maxLength = Math.max(maxLength, currentLength);
+            }
+        }
+
+        return maxLength;
+    }
+}

top-k-frequent-elements/xeulbn.java

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+import java.util.*;
+
+class Solution {
+    public int[] topKFrequent(int[] nums, int k) {
+        Map<Integer,Integer> countMap = new HashMap<>();
+
+        for(int i=0;i<nums.length;i++){
+            countMap.put(nums[i],countMap.getOrDefault(nums[i],0)+1);
+        }
+        PriorityQueue<Integer> pq = new PriorityQueue<>(
+                (a,b)-> countMap.get(a) - countMap.get(b)
+        );
+
+        for(int num: countMap.keySet()){
+            pq.offer(num);
+
+            if(pq.size()>k){
+                pq.poll();
+            }
+        }
+
+        int[] answer = new int[k];
+
+        for (int i = 0; i < k; i++) {
+            answer[i] = pq.poll();
+        }
+
+        return answer;
+
+    }
+}

two-sum/xeulbn.java

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+import java.util.*;
+
+class Solution {
+    public int[] twoSum(int[] nums, int target) {
+        Map<Integer, Integer> numIndexMap = new HashMap<>();
+
+        for (int i=0; i<nums.length; i++) {
+            int need = target - nums[i];
+            if (numIndexMap.containsKey(need)) {
+                return new int[]{numIndexMap.get(need), i};
+            }
+            numIndexMap.put(nums[i], i);
+        }
+
+        return new int[]{};
+    }
+}