花花酱 LeetCode 1138. Alphabet Board Path

On an alphabet board, we start at position (0, 0), corresponding to character board[0][0].

Here, board = ["abcde", "fghij", "klmno", "pqrst", "uvwxy", "z"].

We may make the following moves:

• 'U' moves our position up one row, if the square exists;
• 'D' moves our position down one row, if the square exists;
• 'L' moves our position left one column, if the square exists;
• 'R' moves our position right one column, if the square exists;
• '!' adds the character board[r][c] at our current position (r, c) to the answer.

Return a sequence of moves that makes our answer equal to target in the minimum number of moves.  You may return any path that does so.

Example 1:

Input: target = "leet"
Output: "DDR!UURRR!!DDD!"

Example 2:

Input: target = "code"
Output: "RR!DDRR!UUL!R!"

Constraints:

• 1 <= target.length <= 100
• target consists only of English lowercase letters.

Solution: Manhattan walk

Compute the coordinates of each char, walk from (x1, y1) to (x2, y2) in Manhattan way.
Be aware of the last row, we can only walk on ‘z’, so go left and up first if needed.

Time complexity: O(26*26 + n)
Space complexity: O(26*26)