Merge pull request #2351 from tedkimdev/tedkimdev/week1

[tedkimdev] WEEK 1 Solutions

Author: tedkimdev

contains-duplicate/tedkimdev.go

@@ -0,0 +1,13 @@
+// Time complexity: O(n)
+// Space complexity: O(n)
+func containsDuplicate(nums []int) bool {
+	seen := map[int]struct{}{}
+
+	for _, num := range nums {
+		if _, ok := seen[num]; ok {
+			return true
+		}
+		seen[num] = struct{}{}
+	}
+	return false
+}

house-robber/tedkimdev.go

@@ -0,0 +1,33 @@
+// Time complexity: O(n)
+// Space complexity: O(1)
+func rob(nums []int) int {
+	if len(nums) == 0 {
+		return 0
+	}
+	if len(nums) == 1 {
+		return nums[0]
+	}
+
+	prevTwo := nums[0]
+	prevOne := Max(nums[0], nums[1])
+
+	for i := 2; i < len(nums); i++ {
+		// take
+		m1 := prevTwo + nums[i]
+		// skip
+		m2 := prevOne
+
+		currentMax := Max(m1, m2)
+		prevTwo = prevOne
+		prevOne = Max(currentMax, prevOne)
+	}
+
+	return prevOne
+}
+
+func Max(a, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}

longest-consecutive-sequence/tedkimdev.go

@@ -0,0 +1,36 @@
+// Time complexity: O(n)
+// Space complexity: O(n)
+func longestConsecutive(nums []int) int {
+	if len(nums) == 0 || len(nums) == 1 {
+		return len(nums)
+	}
+
+	numSet := map[int]struct{}{}
+	for _, num := range nums {
+		numSet[num] = struct{}{}
+	}
+
+	longest := 1
+	for num := range numSet {
+		if _, ok := numSet[num-1]; ok {
+			length := 0
+			for {
+				if _, ok := numSet[num+length]; ok {
+					length++
+				} else {
+					break
+				}
+			}
+			longest = Max(length+1, longest)
+		}
+	}
+
+	return longest
+}
+
+func Max(a, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}

top-k-frequent-elements/tedkimdev.go

@@ -0,0 +1,33 @@
+// Time complexity: O(n)
+// Space complexity: O(n)
+func topKFrequent(nums []int, k int) []int {
+	countByNum := map[int]int{}
+	numsByCount := map[int][]int{}
+	max := 0
+
+	for _, num := range nums {
+		countByNum[num]++
+		if countByNum[num] > max {
+			max = countByNum[num]
+		}
+	}
+
+	for num, count := range countByNum {
+		if _, ok := numsByCount[count]; ok {
+			numsByCount[count] = append(numsByCount[count], num)
+		} else {
+			numsByCount[count] = []int{num}
+		}
+	}
+
+	result := []int{}
+	for i := max; i >= 0; i-- {
+		nums := numsByCount[i]
+		result = append(result, nums...)
+		if len(result) >= k {
+			break
+		}
+	}
+
+	return result[:k]
+}

two-sum/tedkimdev.go

@@ -0,0 +1,21 @@
+package hello
+
+import "testing"
+
+// Time complexity: O(n)
+// Space complexity: O(n)
+func twoSum(nums []int, target int) []int {
+	indexByNum := map[int]int{}
+	for i, num := range nums {
+		diff := target - num
+		if index, ok := indexByNum[diff]; ok {
+			return []int{index, i}
+		}
+		indexByNum[num] = i
+	}
+	return []int{}
+}
+
+func TestTwoSome(t *testing.T) {
+
+}