[iam-edwin] WEEK 01 solutions (#1279)

* contains duplicate

* two sum

* top k frequent elements

* longest consecutive sequence

* house robber

Author: iam-edwin

contains-duplicate/iam-edwin.kt

@@ -0,0 +1,5 @@
+class Solution {
+    fun containsDuplicate(nums: IntArray): Boolean {
+        return nums.size != nums.distinct().size
+    }
+}

house-robber/iam-edwin.java

@@ -0,0 +1,13 @@
+class Solution {
+    public int rob(int[] nums) {
+        int[] result = new int[nums.length + 2];
+
+        for (int index = nums.length - 1; index >= 0; index--) {
+            int robFirst = nums[index] + result[index + 2];
+            int passFirst = result[index + 1];
+            result[index] = Integer.max(robFirst, passFirst);
+        }
+
+        return result[0];
+    }
+}

longest-consecutive-sequence/iam-edwin.java

@@ -0,0 +1,26 @@
+class Solution {
+    public int longestConsecutive(int[] nums) {
+        Set<Integer> set = Arrays.stream(nums)
+            .boxed()
+            .collect(Collectors.toSet());
+
+        return set.stream()
+            .map(num -> {
+                if (set.contains(num - 1)) {
+                    return 0;
+                }
+    
+                int consecutiveLength = 1;
+    
+                while (set.contains(num + 1)) {
+                    consecutiveLength += 1;
+                    num += 1;
+                }
+    
+                return consecutiveLength;
+            })
+            .mapToInt(num -> num)
+            .max()
+            .orElse(0);
+    }
+}

top-k-frequent-elements/iam-edwin.kt

@@ -0,0 +1,10 @@
+class Solution {
+    fun topKFrequent(nums: IntArray, k: Int): IntArray {
+        val countMap = nums.groupBy { it }
+            .mapValues { it.value.size }
+        val sortedList = countMap.entries
+            .sortedByDescending { it.value }
+            .map { it.key }
+        return sortedList.subList(0, k).toIntArray()
+    }
+}

two-sum/iam-edwin.kt

@@ -0,0 +1,22 @@
+class Solution {
+    fun twoSum(nums: IntArray, target: Int): IntArray {
+        val indexMap = nums.mapIndexed { index, num -> num to index }
+            .groupBy({ it.first }, {it.second})
+
+        indexMap.forEach { (firstNum, firstIndicies) ->
+            val secondNum = target - firstNum
+            if (firstNum == secondNum) {
+                if (firstIndicies.size > 1) {
+                    return intArrayOf(firstIndicies[0], firstIndicies[1])
+                }
+            } else {
+                val secondIndicies = indexMap[secondNum]
+                if (secondIndicies != null) {
+                    return intArrayOf(firstIndicies[0], secondIndicies[0])
+                }
+            }
+        }
+        
+        return intArrayOf()
+    }
+}