Search a string as you type the character

Question

I have contacts stored in my mobile. Lets say my contacts are

Ram

Hello

Hi

Feat

Eat

At

When I type letter \'A\' I should get

Answer 1

What I'm thinking to do is, keeping track of the so far matched string. Suppose in the first step, we identify the strings those have "A" in them and we keep trace of the positions of 'A". Then in the next step we only iterate over these strings and instead of searching them full we only check for occurrence of "T" as the next character to "A" we kept trace in the previous step and so on.