Qualcomm interview questions

Write a function that checks if a string has valid parentheses

I was asked 3 coding questions 1) https://leetcode.com/problems/single-number/ 2) https://leetcode.com/problems/count-array-pairs-divisible-by-k/description/ 3) given a string say “AABCCC” , return it as “2A1B3C”. Constraint is say if u have 13'A’s as input , u have to print it as “9A4A”