Valeo Junior Software Developer interview questions

write a program to take an array and return number of zeros and number of ones

there is a number in an array of 201 elements which is repeated, tell me logically how you will find it and if the numbers are between 0 and 200 how can you optimize the code ?

he asked me in first about wireless communications but i told him that i don't know so much about them so, he asked about serial communications : what is the difference between asynchronous and synchronous , draw the clock pulses , what is the SPI , how many lines in it and what is the use for each