week03 (#768)

Author: neverlish

combination-sum/neverlish.go

@@ -0,0 +1,45 @@
+// 시간복잡도: O(n^2)
+// 공간복잡도: O(n^2)
+
+package main
+
+import "testing"
+
+func TestCombinationSum(t *testing.T) {
+	result1 := combinationSum([]int{2, 3, 6, 7}, 7)
+
+	if len(result1) != 2 {
+		t.Errorf("Expected 2, got %d", len(result1))
+	}
+
+	if len(result1[0]) != 3 && len(result1[1]) != 1 {
+		t.Errorf("Expected [[7], [2, 2, 3]], got %v", result1)
+	}
+
+	result2 := combinationSum([]int{2, 3, 5}, 8)
+
+	if len(result2) != 3 {
+		t.Errorf("Expected 3, got %d", len(result2))
+	}
+
+	if len(result2[0]) != 2 && len(result2[1]) != 3 && len(result2[2]) != 3 {
+		t.Errorf("Expected [[2, 2, 2, 2], [2, 3, 3], [3, 5]], got %v", result2)
+	}
+}
+
+func combinationSum(candidates []int, target int) [][]int {
+	dp := make([][][]int, target+1)
+
+	dp[0] = [][]int{{}}
+
+	for _, candidate := range candidates {
+		for i := candidate; i <= target; i++ {
+			for _, combination := range dp[i-candidate] {
+				newCombination := append([]int{candidate}, combination...)
+				dp[i] = append(dp[i], newCombination)
+			}
+		}
+	}
+
+	return dp[target]
+}

maximum-subarray/neverlish.go

@@ -0,0 +1,51 @@
+// 시간복잡도: O(n)
+// 공간복잡도: O(n)
+
+package main
+
+import "testing"
+
+func TestMaxSubArray(t *testing.T) {
+	result1 := maxSubArray([]int{-2,1,-3,4,-1,2,1,-5,4})
+
+	if result1 != 6 {
+		t.Errorf("Expected 6, got %d", result1)
+	}
+
+	result2 := maxSubArray([]int{1})
+
+	if result2 != 1 {
+		t.Errorf("Expected 1, got %d", result2)
+	}
+
+	result3 := maxSubArray([]int{5,4,-1,7,8})
+
+	if result3 != 23 {
+		t.Errorf("Expected 23, got %d", result3)
+	}
+}
+
+func max(nums ...int) int {
+	result := nums[0]
+
+	for _, num := range nums[1:] {
+		if num > result {
+			result = num
+		}
+	}
+
+	return result
+}
+
+func maxSubArray(nums []int) int {
+	dp := make([]int, len(nums))
+
+	dp[0] = nums[0]
+
+	for index, num := range nums[1:] {
+		dp[index+1] = max(0, dp[index]) + num
+		
+	}
+
+	return max(dp...)
+}

product-of-array-except-self/neverlish.go

@@ -0,0 +1,69 @@
+// 시간복잡도 : O(n)
+// 공간복잡도 : O(1)
+
+package main
+
+import "testing"
+
+func TestProductExceptSelf(t *testing.T) {
+	test1 := productExceptSelf([]int{1, 2, 3, 4})
+	if len(test1) != 4 {
+		t.Errorf("Expected 4, got %d", len(test1))
+	}
+
+	if test1[0] != 24 && test1[1] != 12 && test1[2] != 8 && test1[3] != 6 {
+		t.Errorf("Expected [24, 12, 8, 6], got %v", test1)
+	}
+
+	test2 := productExceptSelf([]int{0, 0})
+
+	if len(test2) != 2 {
+		t.Errorf("Expected 2, got %d", len(test2))
+	}
+
+	if test2[0] != 0 && test2[1] != 0 {
+		t.Errorf("Expected [0, 0], got %v", test2)
+	}
+
+	test3 := productExceptSelf([]int{-1,1,0,-3,3})
+	if len(test3) != 5 {
+		t.Errorf("Expected 5, got %d", len(test3))
+	}
+
+	if test3[0] != 0 && test3[1] != 0 && test3[2] != 9 && test3[3] != 0 && test3[4] != 0 {
+		t.Errorf("Expected [0, 0, 9, 0, 0], got %v", test3)
+	}
+}
+
+func productExceptSelf(nums []int) []int {
+	zeroCount := 0
+	product := 1
+
+	for _, num := range nums {
+		if num == 0 {
+			zeroCount++
+		} else {
+			product *= num
+		}
+	}
+
+	result := make([]int, len(nums))
+
+	if zeroCount > 1 {
+		return result
+	}
+
+	for i, num := range nums {
+		if zeroCount == 1 {
+			if num == 0 {
+				result[i] = product
+			} else {
+				result[i] = 0
+			}
+		} else {
+			result[i] = product / num
+		}
+	}
+
+	return result
+}

reverse-bits/neverlish.go

@@ -0,0 +1,22 @@
+// 시간복잡도: O(1)
+// 공간복잡도: O(1)
+
+package main
+
+func reverseBits(num uint32) uint32 {
+  stack := []uint32{}
+
+  for i := 0; i < 32; i++ {
+    stack = append(stack, num&1)
+    num >>= 1
+  }
+
+  result := uint32(0)
+
+  for i := 0; i < 32; i++ {
+    result <<= 1
+    result |= stack[i]
+  }
+
+  return result
+}

two-sum/neverlish.go

@@ -0,0 +1,49 @@
+// 시간복잡도: O(n)
+// 공간복잡도: O(n)
+
+package main
+
+import "testing"
+
+func TestTwoSum(t *testing.T) {
+	result1 := twoSum([]int{2, 7, 11, 15}, 9)
+
+	if len(result1) != 2 {
+		t.Errorf("Expected 2, got %d", len(result1))
+	}
+
+	if result1[0] != 0 && result1[1] != 1 {
+		t.Errorf("Expected [0, 1], got %v", result1)
+	}
+
+	result2 := twoSum([]int{3, 2, 4}, 6)
+
+	if len(result2) != 2 {
+		t.Errorf("Expected 2, got %d", len(result2))
+	}
+
+	if result2[0] != 1 && result2[1] != 2 {
+		t.Errorf("Expected [1, 2], got %v", result2)
+	}
+
+	result3 := twoSum([]int{3, 3}, 6)
+	if len(result3) != 2 {
+		t.Errorf("Expected 2, got %d", len(result3))
+	}
+
+	if result3[0] != 0 && result3[1] != 1 {
+		t.Errorf("Expected [0, 1], got %v", result3)
+	}
+}
+
+func twoSum(nums []int, target int) []int {
+	seen := map[int]int{}
+	for i, num := range nums {
+		complement := target - num
+		if _, ok := seen[complement]; ok {
+			return []int{seen[complement], i}
+		}
+		seen[num] = i
+	}
+	return nil
+}