diff --git a/20201204/main.go b/20201204/main.go
new file mode 100644
index 0000000..d9d50d4
--- /dev/null
+++ b/20201204/main.go
@@ -0,0 +1,37 @@
+package main
+
+import (
+	"sort"
+)
+
+func main() {
+
+}
+
+func countMove(nums []int) int {
+	count := 0
+	l := len(nums)
+	for {
+		if isAllSame(nums) {
+			return count
+		}
+		sort.Ints(nums)
+		for i := 0; i < l-1; i++ {
+			nums[i] += 1
+		}
+		count++
+	}
+}
+
+func isAllSame(nums []int) bool {
+	if len(nums) == 0 {
+		return false
+	}
+	base := nums[0]
+	for _, n := range nums {
+		if base != n {
+			return false
+		}
+	}
+	return true
+}
diff --git a/20201204/main_test.go b/20201204/main_test.go
new file mode 100644
index 0000000..1fb72c7
--- /dev/null
+++ b/20201204/main_test.go
@@ -0,0 +1,39 @@
+package main
+
+import (
+	"testing"
+)
+
+func Test_countMove(t *testing.T) {
+	type args struct {
+		src []int
+	}
+	tests := []struct {
+		name string
+		args args
+		want int
+	}{
+		{
+			"test1",
+			args{[]int{1, 2, 3}},
+			3,
+		},
+		{
+			"test2",
+			args{[]int{1, 1, 1}},
+			0,
+		},
+		{
+			"test3",
+			args{[]int{-100, 0, 100}},
+			300,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := countMove(tt.args.src); got != tt.want {
+				t.Errorf("countMove() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}