解法一：回溯算法 defletterCombinations(digits): ifnotdigits: return[] 定义数字与字母映射关系 phone_map={ '2':['a','b','c'], '3':['d','e','f'], '4':['g','h','i'], '5':['j','k','l'], '6':['m','n','o'], '7':['p','q','r','s'], '8':['t','u','v'], '9':['w','x','y','z'] } res=[] defbacktrack(combination,next_digits): 当没有...