I had two phone interviews back-to-back, each lasting 45 minutes.

Each interview began with a brief introduction of one project from my resume and then continued with technical questions.

The interviewers were very nice to talk with.

1. Given two strings, one is derived by adding some characters into the other. Find all these characters. Example: A='abc', B='aabcde', return ['a','d','e']

2. Given an n×n matrix, each element is either 1 or 0. Find the largest sub-matrix that has 1s at all its corners. Time complexity requirement: O(n^3) Example: M=[0,1,1;0,0,1;0,1,1], return [[0,1],[2,2]] (the left-top and right-bottom corners).