Microsoft Full Stack Developer interview questions

1) Given an array of N (natural) integers. return the largest number K (K>0) only if K and -K exist in the array, if there's no such number return 0. For example if arr=[4,-4, 3, -3, 2], should return 4, and arr=[-2,0,0,-3] should return 0. I think the algorithm should solve this in O(N). 2) Given a string S of N letters, we want to return the alphabetically largest letter that occurs in both lowercase and uppercase in S, or decide that there's no such letter. For example S=aaBabcDaA, should return "B", else should return "NO". For example S=Codility, return "NO". 3) A very long question about Jafar & Aladdin, pawn game. Find the maximum pawns owned by Aladdin that Jafar can beat in his turn (given a board N x N). Sorry.