diff --git a/day20/day20.go b/day20/day20.go
new file mode 100644
index 0000000..13f1e28
--- /dev/null
+++ b/day20/day20.go
@@ -0,0 +1,184 @@
+package day20
+
+import (
+	"fmt"
+	"strings"
+)
+
+const (
+	UNTYPED      = "?"
+	FLIP_FLOP    = "%"
+	BROADCASDTER = "b"
+	CONJUNCTION  = "&"
+	LOW          = 0
+	HIGH         = 1
+)
+
+type Module struct {
+	kind     string
+	name     string
+	status   bool
+	ouputs   []string
+	inputs   []string
+	inputMem map[string]int
+}
+
+type Pulse struct {
+	kind int
+	src  string
+	dst  string
+}
+
+func parseModules(lines []string) map[string]*Module {
+	modules := map[string]*Module{}
+	modulesByOrderOfAppearance := []*Module{}
+
+	for _, line := range lines {
+		kind := string(line[0])
+		parts := strings.Split(line, " -> ")
+		name := parts[0][1:]
+		outputs := strings.Split(parts[1], ", ")
+
+		if kind == "b" {
+			name = "b" + name
+		}
+
+		module := &Module{kind, name, false, outputs, []string{}, map[string]int{}}
+		modules[name] = module
+		modulesByOrderOfAppearance = append(modulesByOrderOfAppearance, module)
+	}
+
+	// setup inputs
+	for _, module := range modulesByOrderOfAppearance {
+		for _, outputName := range module.ouputs {
+			m, ok := modules[outputName]
+
+			if !ok {
+				// create ad'hoc untyped module
+				m = &Module{UNTYPED, outputName, false, []string{}, []string{}, map[string]int{}}
+				modules[outputName] = m
+				modulesByOrderOfAppearance = append(modulesByOrderOfAppearance, m)
+			}
+
+			m.inputs = append(m.inputs, module.name)
+			m.inputMem[module.name] = LOW
+		}
+	}
+
+	return modules
+}
+
+func runSim(modules map[string]*Module, pulseQueue []*Pulse, count int) (int, int) {
+	countLow := 0
+	countHigh := 0
+
+	for len(pulseQueue) > 0 {
+
+		pulse := pulseQueue[0]
+		pulseQueue[0] = nil
+		pulseQueue = pulseQueue[1:]
+
+		module := modules[pulse.dst]
+
+		switch module.kind {
+		case BROADCASDTER:
+			for _, dst := range module.ouputs {
+				newPulse := &Pulse{pulse.kind, module.name, dst}
+				pulseQueue = append(pulseQueue, newPulse)
+				if newPulse.kind == LOW {
+					countLow++
+				} else {
+					countHigh++
+				}
+			}
+
+		case FLIP_FLOP:
+			if pulse.kind == LOW {
+				var pulseKind int
+				if module.status {
+					pulseKind = LOW
+				} else {
+					pulseKind = HIGH
+				}
+				module.status = !module.status // flip status
+
+				for _, dst := range module.ouputs {
+					newPulse := &Pulse{pulseKind, module.name, dst}
+					pulseQueue = append(pulseQueue, newPulse)
+					if newPulse.kind == LOW {
+						countLow++
+					} else {
+						countHigh++
+					}
+				}
+			}
+
+		case CONJUNCTION:
+			if pulse.kind == HIGH && module.name == "qn" {
+				fmt.Println("qn from ", pulse.src, " :  ", count)
+			}
+			module.inputMem[pulse.src] = pulse.kind
+			allHigh := true
+			for _, v := range module.inputMem {
+				if v == LOW {
+					allHigh = false
+					break
+				}
+			}
+
+			var pulseKind int
+			if allHigh {
+				pulseKind = LOW
+			} else {
+				pulseKind = HIGH
+			}
+
+			for _, dst := range module.ouputs {
+				newPulse := &Pulse{pulseKind, module.name, dst}
+				pulseQueue = append(pulseQueue, newPulse)
+				if newPulse.kind == LOW {
+					countLow++
+				} else {
+					countHigh++
+				}
+			}
+
+		case UNTYPED:
+			module.status = pulse.kind == HIGH
+		}
+
+	}
+
+	return countLow, countHigh
+}
+
+func Part1(lines []string, pressCount int) (map[string]*Module, int) {
+	modules := parseModules(lines)
+
+	sumLow := 0
+	sumHigh := 0
+
+	for i := 0; i < pressCount; i++ {
+		queue := []*Pulse{}
+		queue = append(queue, &Pulse{LOW, "button", "broadcaster"})
+		countLow, countHigh := runSim(modules, queue, i+1)
+		countLow++
+
+		sumLow += countLow
+		sumHigh += countHigh
+	}
+
+	return modules, sumLow * sumHigh
+}
+
+func Part2(lines []string, pressCount int) (map[string]*Module, int) {
+	modules := parseModules(lines)
+
+	for i := 0; i < pressCount; i++ {
+		queue := []*Pulse{}
+		queue = append(queue, &Pulse{LOW, "button", "broadcaster"})
+		runSim(modules, queue, i+1)
+	}
+
+	return modules, 0
+}
diff --git a/day20/day20_test.go b/day20/day20_test.go
new file mode 100644
index 0000000..dea92a3
--- /dev/null
+++ b/day20/day20_test.go
@@ -0,0 +1,125 @@
+package day20
+
+import (
+	"testing"
+
+	"gitea.paas.celticinfo.fr/oabrivard/aoc2023/utils"
+)
+
+func TestParseModule(t *testing.T) {
+	lines := []string{
+		`broadcaster -> a, b, c`,
+		`%a -> b`,
+		`%b -> c`,
+		`%c -> inv`,
+		`&inv -> a`,
+	}
+
+	result := parseModules(lines)
+
+	if len(result) != 5 {
+		t.Fatalf("expected 5, got %d", len(result))
+	}
+}
+
+func Test1Part1(t *testing.T) {
+	lines := []string{
+		`broadcaster -> a, b, c`,
+		`%a -> b`,
+		`%b -> c`,
+		`%c -> inv`,
+		`&inv -> a`,
+	}
+
+	result, count := Part1(lines, 1)
+
+	if count != 32 {
+		t.Fatalf("expected 32, got %d", count)
+	}
+
+	if result["a"].status || result["b"].status || result["c"].status {
+		t.Fatalf("expected flip-flop a, b and c to be off, got %v %v %v", result["a"].status, result["b"].status, result["c"].status)
+	}
+}
+
+func Test2Part1(t *testing.T) {
+	lines := []string{
+		`broadcaster -> a, b, c`,
+		`%a -> b`,
+		`%b -> c`,
+		`%c -> inv`,
+		`&inv -> a`,
+	}
+
+	_, count := Part1(lines, 1000)
+
+	if count != 32000000 {
+		t.Fatalf("expected 32000000, got %d", count)
+	}
+}
+
+func Test3Part1(t *testing.T) {
+	lines := []string{
+		"broadcaster -> a",
+		"%a -> inv, con",
+		"&inv -> b",
+		"%b -> con",
+		"&con -> output",
+	}
+
+	result, _ := Part1(lines, 3)
+
+	if !result["output"].status || !result["a"].status || result["b"].status {
+		t.Fatalf("expected flip-flop a to be on, b to be off and output to be on, got %v %v %v", result["a"].status, result["b"].status, result["output"].status)
+	}
+
+	result, _ = Part1(lines, 4)
+
+	if !result["output"].status || result["a"].status || result["b"].status {
+		t.Fatalf("expected flip-flop a and b to be off and output to be on, got %v %v %v", result["a"].status, result["b"].status, result["output"].status)
+	}
+}
+
+func Test4Part1(t *testing.T) {
+	lines := []string{
+		"broadcaster -> a",
+		"%a -> inv, con",
+		"&inv -> b",
+		"%b -> con",
+		"&con -> output",
+	}
+
+	_, count := Part1(lines, 1000)
+
+	if count != 11687500 {
+		t.Fatalf("expected 11687500, got %d", count)
+	}
+}
+
+func TestPart1WithInput(t *testing.T) {
+	lines := utils.ReadLines("input.txt")
+
+	_, count := Part1(lines, 1000)
+
+	if count != 925955316 {
+		t.Fatalf("expected 925955316, got %d", count)
+	}
+}
+
+func TestPart2WithInput(t *testing.T) {
+	lines := utils.ReadLines("input.txt")
+
+	Part2(lines, 5000)
+
+	// use firt four different values printed during simulation that starts with "qn from"
+	// then find the LCM of the values. The LCM is the solution to this problem.
+	// Found it thanks to explanation from jwezorek and JuniorBirdman1115 on
+	//  https://www.reddit.com/r/adventofcode/comments/18mmfxb/2023_day_20_solutions/
+	/*
+		qn from  jx  :   3907
+		qn from  qz  :   3911
+		qn from  tt  :   3931
+		qn from  cq  :   4021
+		LCM is 241528477694627 (computed it with https://www.calculatorsoup.com/calculators/math/lcm.php)
+	*/
+}
diff --git a/day20/input.txt b/day20/input.txt
new file mode 100644
index 0000000..436fa87
--- /dev/null
+++ b/day20/input.txt
@@ -0,0 +1,58 @@
+%cg -> mt, hb
+%sp -> xm
+%nr -> hf, mt
+broadcaster -> tl, gd, zb, gc
+&qz -> qn
+%df -> hd
+%vg -> rm, kx
+%gm -> mt, md
+%ls -> hc
+%lq -> zq, fx
+&zd -> bz, kg, zb, lf, sq, zk, jx
+%lz -> mt
+%sq -> zk
+%zn -> kx, tc
+&zq -> mb, hc, qz, ql, tl, ls
+&mt -> zm, tt, mh, gd, md
+%lm -> mb, zq
+%hf -> mt, sm
+%hb -> mh, mt
+%rm -> kx
+%gc -> kx, sp
+&cq -> qn
+%mh -> jt
+%zm -> nr
+%xm -> kx, ld
+&jx -> qn
+&qn -> rx
+%mp -> qt, kx
+%zk -> vj
+%hd -> mp, kx
+%tl -> zq, hl
+%zb -> zd, ph
+%cl -> zd
+&tt -> qn
+%ld -> zn
+%js -> lq, zq
+%sm -> mt, lz
+%qt -> vg, kx
+%md -> cg
+%vj -> bz, zd
+%qs -> zd, fs
+%mb -> ps
+&kx -> cq, gc, sp, df, ld
+%hc -> lm
+%tc -> df, kx
+%ps -> js, zq
+%fs -> qc, zd
+%hl -> jj, zq
+%bz -> qs
+%jj -> zq, ql
+%ql -> ls
+%ph -> kg, zd
+%qc -> cl, zd
+%lf -> sq
+%kg -> lf
+%fx -> zq
+%jt -> zm, mt
+%gd -> gm, mt