1 Answer

I have the New Living Translation version of the Life Application Bible.  The study portion says:
"This is both the longest psalm and the longest chapter in the Bible. It may have been written by Ezra  after the Temple was rebuilt (Ezra 6:14, 15)as a repetitive meditation on the beauty of God's Word and hot it helps us stay pure and grow in faith. Psalm 119 has 22 carefully constructed sections, each corresponding to a different letter in the Hebrew alphabet and each verse beginning with the letter of its section. Almost every verse mentions God's Word. Such repetition was common in the Hebrew culture. People did not have personal copies of the Scriptures to read, so God's people memorized his Word and passed it along orally. The structure of this psalm allowed for easy memorization."  
The letters in my version of Psalm 119 are:  Aleph, Beth, Gimel, Daleth, He, Waw, Zayin, Heth, Teth, Yodh, Kaph, Lamedh, Mem, Nun, Samekh, Ayin, Pe, Tsadhe, Qoph, Resh, Shin, Taw.    The sixth one is "Waw".
I hope this helps.