[hyunpill3] WEEK 01 Solutions

contains-duplicate/hyunpill3.java

@@ -0,0 +1,12 @@
+class Solution {
+    public boolean containsDuplicate(int[] nums) {
+        HashSet<Integer> set = new HashSet<>();
+        for (int num : nums) {
+            if (set.contains(num)) {
+                return true;
+            }
+            set.add(num);
+        }
+        return false;
+    }
+}

house-robber/hyunpill3.java

@@ -0,0 +1,15 @@
+class Solution {
+    public int rob(int[] nums) {
+        int next = 0;
+        int next2 = 0;
+
+        for (int num : nums) {
+            int current = Math.max(next, next2 + num);
+
+            next2 = next;
+            next = current;
+        }
+
+        return next;
+    }
+}

longest-consecutive-sequence/hyunpill3.java

@@ -0,0 +1,26 @@
+class Solution {
+    public int longestConsecutive(int[] nums) {
+        Set<Integer> set = new HashSet<>();
+        for (int num : nums) {
+            set.add(num);
+        }
+
+        int res = 0;
+
+        for (int num : set) {
+            if (!set.contains(num - 1)) {
+                int current = num;
+                int count = 1;
+
+                while (set.contains(current + 1)) {
+                    current++;
+                    count++;
+                }
+
+                res = Math.max(res, count);
+            }
+        }
+
+        return res;
+    }
+}

top-k-frequent-elements/hyunpill3.java

@@ -0,0 +1,17 @@
+class Solution {
+    public int[] topKFrequent(int[] nums, int k) {
+        List<Integer> list = new ArrayList<>();
+        Arrays.stream(nums)
+            .boxed()
+            .collect(Collectors.groupingBy(x -> x))
+            .entrySet()
+            .stream()
+            .sorted(Map.Entry.comparingByValue((o1, o2) -> Integer.compare(o2.size(), o1.size())))
+            .forEachOrdered(x -> {
+                if (list.size() < k) 
+                    list.add(x.getKey());
+            });
+
+        return list.stream().mapToInt(Integer::intValue).toArray();
+    }
+}

two-sum/hyunpill3.java

@@ -0,0 +1,12 @@
+class Solution {
+    public int[] twoSum(int[] nums, int target) {
+        HashMap<Integer, Integer> map = new HashMap<>();
+        for (int i = 0; i < nums.length; i++) {
+            int num2 = target - nums[i];
+            if (map.containsKey(num2)) {
+                return new int[] { map.get(num2), i};
+            }
+            map.put(nums[i], i)
+        }
+    }
+}