Implement encoding validation and grid shortest path

Part A — Byte-encoding validation: You are given an array of integers in [0, 255] representing bytes. Determine whether the sequence encodes valid characters under a variable-length scheme where: ( 1) A single-byte character starts with leading bit 0; ( 2) A multi-byte character uses k bytes for k in {2,3,4}, whose first byte has a prefix of exactly k ones followed by a zero (e.g., 110xxxxx, 1110xxxx, 11110xxx); ( 3) Each continuation byte starts with the bit pattern 10xxxxxx; ( 4) The sequence cannot end mid-character. Return true/false and specify the time and space complexity of your approach. Part B — 8-neighbor grid shortest path: Given an n×n grid of 0s (open) and 1s (blocked), find the length of the shortest path from (0, 0) to (n−1,n− 1) moving in any of the 8 directions to adjacent open cells. Count both start and end cells in the length; if no path exists, return −1. Discuss the algorithm and its complexity.