[juhui-jeong] WEEK 1 Solutions

contains-duplicate/juhui-jeong.java

@@ -0,0 +1,38 @@
+/*
+
+// 첫번째 풀이
+class Solution {
+    public boolean containsDuplicate(int[] nums) {
+        for (int i=0; i < nums.length; i++) {
+            for (int j=i+1; j < nums.length; j++) {
+                if (nums[i] == nums[j]) return true;
+            }
+        }
+        return false;
+    }
+}
+
+// 두번째 풀이
+class Solution {
+    public boolean containsDuplicate(int[] nums) {
+        Set set = new HashSet<Integer>();
+        for (int i=0; i < nums.length; i++) {
+            set.add(nums[i]);
+        }
+
+        if (set.size() != nums.length) return true;
+        return false;
+    }
+}
+
+*/
+
+class Solution {
+    public boolean containsDuplicate(int[] nums) {
+        Set<Integer> set = new HashSet<>();        
+        for (int i=0; i < nums.length; i++) {
+            if (!set.add(nums[i])) return true;
+        }
+        return false;
+    }
+}

longest-consecutive-sequence/juhui-jeong.java

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+class Solution {
+    public int longestConsecutive(int[] nums) {
+        if(nums == null || nums.length == 0) return 0;
+        Arrays.sort(nums);
+
+        int maxLen = 1;
+        int curLen = 1;
+
+        for(int i = 1; i < nums.length; i++) {
+            if (nums[i] == nums[i-1]) {
+                // 중복 건너뛰기
+                continue;
+            }
+
+            if (nums[i] == nums[i-1] +1) {
+                curLen++;
+            } else {
+                maxLen = Math.max(maxLen, curLen);
+                curLen = 1;
+            }
+        }
+
+        return Math.max(maxLen, curLen);
+    }
+}

top-k-frequent-elements/juhui-jeong.java

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+class Solution {
+    public int[] topKFrequent(int[] nums, int k) {
+        Map<Integer, Integer> map = new HashMap<>();
+
+        for (int i = 0; i< nums.length; i++) {
+            if (map.containsKey(nums[i])) {
+                map.put(nums[i], map.get(nums[i])+1);
+            } else {
+                map.put(nums[i], 1);
+            }
+        }
+
+        List<Map.Entry<Integer, Integer>> entryList = new LinkedList<>(map.entrySet());
+        entryList.sort(Map.Entry.comparingByValue(Collections.reverseOrder()));
+
+        int[] result = new int[k];
+
+        for(int i =0; i < k; i++) {
+            result[i] = entryList.get(i).getKey();
+        }
+
+        return result;
+    }
+}

two-sum/juhui-jeong.java

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+class Solution {
+    public int[] twoSum(int[] nums, int target) {
+        for(int i = 0; i < nums.length; i++) {
+            for(int j=i+1; j < nums.length; j++) {
+                if (nums[i] + nums[j] == target) {
+                    return new int[] {i, j};
+                }
+            }
+        }
+        return new int[0];
+    }
+}