12. The input method according to claim 11 , wherein the step of obtaining the four input symbol representative numbers representing the phonetic notation comprises: if the phonetic notation includes one of the three head vowels, taking an head vowel representative number corresponding to one of the included three head vowels as one of the four input symbol representative numbers; and if the phonetic notation does not include any of the three head vowels, taking a pre-determined representative number as one of the four input symbol representative numbers.
12. The input method according to claim 11 , wherein the step of obtaining the four input symbol representative numbers representing the phonetic notation comprises: if the phonetic notation includes one of the three head vowels, taking an head vowel representative number corresponding to one of the included three head vowels as one of the four input symbol representative numbers; and if the phonetic notation does not include any of the three head vowels, taking a pre-determined representative number as one of the four input symbol representative numbers. 13. The input method according to claim 12 , wherein the step of obtaining the four input symbol representative numbers representing the phonetic notation comprises: if the phonetic notation includes one of the 13 vowels, taking an vowel representative number corresponding to one of the included 13 vowels as one of the four input symbol representative numbers; and if the phonetic notation does not include any of the 13 vowels, taking a pre-determined representative number as one of the four input symbol representative numbers.