[ymir0804] WEEK 01 solutions

contains-duplicate/ymir0804.java

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+import java.util.Arrays;
+import java.util.List;
+import java.util.stream.Collectors;
+
+class Solution {
+    public boolean containsDuplicate(int[] nums) {
+        List<Integer> list = Arrays.stream(nums).boxed().collect(Collectors.toList());
+        for (int i : nums) {
+            int idx = list.indexOf(i);
+            if (idx == -1) {
+                continue;
+            }
+            list.remove(idx);
+            if (list.contains(i)) {
+                return true;
+            }
+        }
+        return false;
+    }
+}

top-k-frequent-elements/ymir0804.java

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+import java.util.*;
+import java.util.stream.Collectors;
+
+class Solution {
+    public int[] topKFrequent(int[] nums, int k) {
+        Set<Integer> unique = Arrays.stream(nums).boxed().collect(Collectors.toSet());
+        Map<Integer, Integer> value = new HashMap<>();
+        for (int n : unique) {
+            int cnt = 0;
+            for (int m : nums) {
+                if (n == m) {
+                    cnt++;
+                }
+            }
+            value.put(n, cnt);
+        }
+        List<Map.Entry<Integer, Integer>> sortedByValueDesc = value.entrySet()
+                .stream()
+                .sorted(Map.Entry.comparingByValue(Comparator.reverseOrder()))
+                .toList();
+        return sortedByValueDesc.stream()
+                .limit(k)
+                .map(Map.Entry::getKey)
+                .mapToInt(Integer::intValue)
+                .toArray();
+    }
+}

two-sum/ymir0804.java

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+import java.util.HashMap;
+import java.util.Map;
+
+class Solution {
+    public int[] twoSum(int[] nums, int target) {
+        // 시간 복잡도를 생각해서 HashMap을 사용
+
+        Map<Integer, Integer> idx = new HashMap<>();
+        for (int i = 0; i < nums.length; i++) {
+            int c = target - nums[i];
+            if (idx.containsKey(c)) {
+                return new int[]{idx.get(c), i};
+            }
+            idx.put(nums[i], i);
+        }
+        return new int[]{};
+    }
+}