[JEONGBEOMKO] WEEK 01 solutions

contains-duplicate/jeongbeomko.java

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+import java.util.HashSet;
+
+class Solution {
+    public boolean containsDuplicate(int[] nums) {
+        HashSet<Integer> numSet  = new HashSet<>();
+
+        for (int i = 0; i < nums.length; i++) {
+
+            if (numSet.contains(nums[i])) {
+                return true;
+            }
+            numSet.add(nums[i]);
+        }
+
+        return false;
+    }
+}

house-robber/JEONGBEOMKO.java

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+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/JEONGBEOMKO.java

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+import java.util.HashMap;
+import java.util.Map;
+
+class Solution {
+
+    public boolean containsDuplicate(int[] nums) {
+
+        Map<Integer, Integer> countMap = new HashMap<>();
+
+        for (int i = 0; i < nums.length; i++) {
+            countMap.put(nums[i], countMap.getOrDefault(nums[i] , 0) + 1);
+        }
+
+        for (Map.Entry<Integer, Integer> map : countMap.entrySet()) {
+            if (map.getValue() >= 2) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+}

top-k-frequent-elements/JEONGBEOMKO.java

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+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.Map;
+
+class Solution {
+    public int[] topKFrequent(int[] nums, int k) {
+
+        Map<Integer, Integer> frequencyMap = new HashMap<>();
+        for(int num : nums) {
+            frequencyMap.put(num, frequencyMap.getOrDefault(num, 0) + 1);
+        }
+
+        Map.Entry<Integer, Integer>[] arr = new Map.Entry[frequencyMap.size()];
+        Iterator<Map.Entry<Integer, Integer>> iterator = frequencyMap.entrySet().iterator();
+        for (int i=0; i<arr.length; i++) {
+            arr[i] = iterator.next();
+        }
+
+        Arrays.sort(arr, (e1, e2) -> e2.getValue() - e1.getValue());
+
+        int[] answer = new int[k];
+        for (int i=0; i<k; i++) {
+            answer[i] = arr[i].getKey();
+        }
+
+        return answer;
+    }
+}

two-sum/JEONGBEOMKO.java

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+import java.util.HashMap;
+import java.util.Map;
+
+class Solution {
+    public int[] twoSum(int[] nums, int target) {
+        Map<Integer, Integer> numberMap = new HashMap<>();
+        for (int i=0; i<nums.length; i++) {
+            numberMap.put(nums[i], i);
+        }
+
+        for(int i=0; i<nums.length; i++) {
+            int operand = target - nums[i];
+            if (numberMap.containsKey(operand) && numberMap.get(operand) != i) { // 자기 자신은 제외
+                return new int[] { numberMap.get(target - nums[i]), i };
+            }
+        }
+
+        return new int[] {};
+    }
+}