From 6e3185914e8190da0f85e9461a80a584a31e1d97 Mon Sep 17 00:00:00 2001
From: Angelica Hjelm Gardner <angelicahjelmgardner@gmail.com>
Date: Mon, 9 Mar 2026 20:49:16 +0300
Subject: [PATCH] feat(euler): solve problem 001 multiples of 3 and 5

---
 .github/workflows/go-test.yaml           |  6 +++---
 .github/workflows/lint.yaml              | 14 +++++++------
 .golangci.yaml                           | 26 ++++++++++++++++--------
 README.md                                | 11 +---------
 go.mod                                   |  2 +-
 {ProjectEuler => projecteuler}/README.md |  0
 projecteuler/problem_001.go              | 14 +++++++++++++
 projecteuler/problem_001_test.go         | 25 +++++++++++++++++++++++
 8 files changed, 70 insertions(+), 28 deletions(-)
 rename {ProjectEuler => projecteuler}/README.md (100%)
 create mode 100644 projecteuler/problem_001.go
 create mode 100644 projecteuler/problem_001_test.go

diff --git a/.github/workflows/go-test.yaml b/.github/workflows/go-test.yaml
index 9cc1aae..aad9ebf 100644
--- a/.github/workflows/go-test.yaml
+++ b/.github/workflows/go-test.yaml
@@ -10,12 +10,12 @@ jobs:
 
     steps:
     - name: Checkout code
-      uses: actions/checkout@v2
+      uses: actions/checkout@v4
 
     - name: Set up Go
-      uses: actions/setup-go@v3
+      uses: actions/setup-go@v5
       with:
-        go-version: '1.21'
+        go-version: '1.24'
 
     - name: Install dependencies
       run: go mod tidy
diff --git a/.github/workflows/lint.yaml b/.github/workflows/lint.yaml
index 1ad1345..bd2ea1f 100644
--- a/.github/workflows/lint.yaml
+++ b/.github/workflows/lint.yaml
@@ -12,16 +12,18 @@ jobs:
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
 
       - name: Set up Go
-        uses: actions/setup-go@v2
+        uses: actions/setup-go@v5
         with:
-          go-version: '1.21'
+          go-version: '1.24'
+          cache: true
 
-      - name: Install golangci-lint
-        run: |
-          curl -sSfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh | sh -s -- -b $(go env GOPATH)/bin v1.59.1
+      - name: Run golangci-lint
+        uses: golangci/golangci-lint-action@v6
+        with:
+          version: v1.64.5
 
       - name: Print Go environment
         run: |
diff --git a/.golangci.yaml b/.golangci.yaml
index bbd5216..5670271 100644
--- a/.golangci.yaml
+++ b/.golangci.yaml
@@ -1,7 +1,7 @@
 linters:
+  disable-all: false
   enable:
     - errorlint
-    #- godot
     - goimports
     - misspell
     - nolintlint
@@ -9,21 +9,31 @@ linters:
     - testifylint
     - unconvert
     - durationcheck
-    - exportloopref
     - nilerr
     - whitespace
     - unparam
     - tagalign
     - stylecheck
     - gosec
-    #- gofumpt
     - perfsprint
     - nestif
     - noctx
     - prealloc
     - depguard
-    # - revive
-    # - gocritic
-    # - wastedassign
-    # - goconst
-    # - gomnd
\ No newline at end of file
+    - gocritic
+    - bodyclose
+
+linters-settings:
+  depguard:
+    rules:
+      main:
+        deny:
+          - pkg: "io/ioutil"
+            desc: "ioutil is deprecated, use os or io instead"
+
+  nestif:
+    min-complexity: 5
+
+run:
+  timeout: 5m
+  tests: true
\ No newline at end of file
diff --git a/README.md b/README.md
index beb14a1..2b107dc 100644
--- a/README.md
+++ b/README.md
@@ -30,16 +30,7 @@ The test cases should test both solutions.
 ### Solution Template
 
 ```go
-/*
-[Issue title]
-
-// Time complexity:     O(n)
-// Space complexity:    O(n)
-func ImprovedSolution() {
-
-*/
-
-package challenge
+package challengeName
 
 // Time complexity:     O(n)
 // Space complexity:    O(n)
diff --git a/go.mod b/go.mod
index cc6e73a..c5e9d49 100644
--- a/go.mod
+++ b/go.mod
@@ -1,3 +1,3 @@
 module github.com/angelicagardner/coding-challenges
 
-go 1.21.1
+go 1.24
diff --git a/ProjectEuler/README.md b/projecteuler/README.md
similarity index 100%
rename from ProjectEuler/README.md
rename to projecteuler/README.md
diff --git a/projecteuler/problem_001.go b/projecteuler/problem_001.go
new file mode 100644
index 0000000..7eae9d3
--- /dev/null
+++ b/projecteuler/problem_001.go
@@ -0,0 +1,14 @@
+package projecteuler
+
+// Time complexity:     O(1)
+// Space complexity:    O(1)
+func Solution(limit int) int {
+	n := limit - 1
+
+	sumMultiples := func(k int) int {
+		p := n / k
+		return k * (p * (p + 1)) / 2
+	}
+
+	return sumMultiples(3) + sumMultiples(5) - sumMultiples(15)
+}
diff --git a/projecteuler/problem_001_test.go b/projecteuler/problem_001_test.go
new file mode 100644
index 0000000..519447f
--- /dev/null
+++ b/projecteuler/problem_001_test.go
@@ -0,0 +1,25 @@
+package projecteuler
+
+import "testing"
+
+func TestSolution(t *testing.T) {
+	t.Run("limit 10", func(t *testing.T) {
+		limit := 10
+		expected := 23
+		got := Solution(limit)
+
+		if got != expected {
+			t.Errorf("Solution(%d) = %d; want %d", limit, got, expected)
+		}
+	})
+
+	t.Run("limit 1000", func(t *testing.T) {
+		limit := 1000
+		expected := 233168
+		got := Solution(limit)
+
+		if got != expected {
+			t.Errorf("Solution(%d) = %d; want %d", limit, got, expected)
+		}
+	})
+}