[YoungDaLee] WEEK 01 solutions

contains-duplicate/youngDaLee.go

@@ -0,0 +1,12 @@
+package youngDaLee
+
+func containsDuplicate(nums []int) bool {
+	numMap := make(map[int]bool)
+	for _, num := range nums {
+		if _, exists := numMap[num]; exists {
+			return true
+		}
+		numMap[num] = true
+	}
+	return false
+}

house-robber/youngDaLee.go

@@ -0,0 +1,27 @@
+package youngDaLee
+
+func rob(nums []int) int {
+	if len(nums) == 0 {
+		return 0
+	}
+	if len(nums) == 1 {
+		return nums[0]
+	}
+
+	dp := make([]int, len(nums))
+	dp[0] = nums[0]
+	dp[1] = max(nums[0], nums[1])
+
+	for i := 2; i < len(nums); i++ {
+		dp[i] = max(dp[i-1], dp[i-2]+nums[i])
+	}
+
+	return dp[len(nums)-1]
+}
+
+func max(a, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}

longest-consecutive-sequence/youngDaLee.go

@@ -0,0 +1,28 @@
+package youngDaLee
+
+func longestConsecutive(nums []int) int {
+	numSet := make(map[int]bool)
+	for _, num := range nums {
+		numSet[num] = true
+	}
+
+	longestStreak := 0
+
+	for num := range numSet {
+		if !numSet[num-1] {
+			currentNum := num
+			currentStreak := 1
+
+			for numSet[currentNum+1] {
+				currentNum++
+				currentStreak++
+			}
+
+			if currentStreak > longestStreak {
+				longestStreak = currentStreak
+			}
+		}
+	}
+
+	return longestStreak
+}

top-k-frequent-elements/youngDaLee.go

@@ -0,0 +1,31 @@
+package youngDaLee
+
+import "sort"
+
+func topKFrequent(nums []int, k int) []int {
+	frequencyMap := make(map[int]int)
+	for _, num := range nums {
+		frequencyMap[num]++
+	}
+
+	type freqPair struct {
+		num   int
+		count int
+	}
+
+	freqPairs := make([]freqPair, 0, len(frequencyMap))
+	for num, count := range frequencyMap {
+		freqPairs = append(freqPairs, freqPair{num, count})
+	}
+
+	sort.Slice(freqPairs, func(i, j int) bool {
+		return freqPairs[i].count > freqPairs[j].count
+	})
+
+	result := make([]int, k)
+	for i := 0; i < k; i++ {
+		result[i] = freqPairs[i].num
+	}
+
+	return result
+}

two-sum/youngDaLee.go

@@ -0,0 +1,14 @@
+package youngDaLee
+
+func twoSum(nums []int, target int) []int {
+	numMap := make(map[int]int)
+	for i, num := range nums {
+		sub := target - num
+		if j, exists := numMap[sub]; exists {
+			return []int{j, i}
+		}
+		numMap[num] = i
+	}
+
+	return []int{}
+}