diff --git a/20201224/main.go b/20201224/main.go
new file mode 100644
index 0000000..eec3b38
--- /dev/null
+++ b/20201224/main.go
@@ -0,0 +1,37 @@
+package main
+
+func main() {
+
+}
+
+func isEcho(s string) bool {
+	var sc []uint8
+	for i := 0; i < len(s); i++ {
+		c := s[i]
+		if isAlphabetAndDigit(c) {
+			if c <= 'Z' && c >= 'A' {
+				c += 'a' - 'A'
+			}
+			sc = append(sc, c)
+		}
+	}
+	if len(sc) == 0 {
+		return true
+	}
+	l, r := 0, len(sc)-1
+	for {
+		if l >= r {
+			break
+		}
+		if sc[l] != sc[r] {
+			return false
+		}
+		l++
+		r--
+	}
+	return true
+}
+
+func isAlphabetAndDigit(c uint8) bool {
+	return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || (c >= '0' && c <= '9')
+}
diff --git a/20201224/main_test.go b/20201224/main_test.go
new file mode 100644
index 0000000..e774d5b
--- /dev/null
+++ b/20201224/main_test.go
@@ -0,0 +1,71 @@
+package main
+
+import "testing"
+
+func Test_isAlphabetAndDigit(t *testing.T) {
+	type args struct {
+		c uint8
+	}
+	tests := []struct {
+		name string
+		args args
+		want bool
+	}{
+		{
+			"test1",
+			args{c: 'a'},
+			true,
+		},
+		{
+			"test2",
+			args{c: '1'},
+			true,
+		},
+		{
+			"test3",
+			args{c: '-'},
+			false,
+		},
+		{
+			"test4",
+			args{c: ','},
+			false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := isAlphabetAndDigit(tt.args.c); got != tt.want {
+				t.Errorf("isAlphabet() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func Test_isEcho(t *testing.T) {
+	type args struct {
+		s string
+	}
+	tests := []struct {
+		name string
+		args args
+		want bool
+	}{
+		{
+			"test1",
+			args{s: "A man, a plan, a canal: Panama"},
+			true,
+		},
+		{
+			"test2",
+			args{s: "race a car"},
+			false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := isEcho(tt.args.s); got != tt.want {
+				t.Errorf("isEcho() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}