传教士与野人问题。完美版。getStrategy函数参数是N和k，返回的是一个字符串数组，代表一个状态序列，数组中的每一个元素代表一个状态，每一个状态表示为（a，b，c），其中a表示左岸的传教士数目，b表示左岸的野人数目，c表示船是否在左岸，c=1为船在左岸，c=0为船在右岸。如果问题无解，返回只有一个元素 “no solution”的数组。-Missionaries and savages the problem. Perfect version. getStrategy function parameters are N and k, returns a string array, on behalf of a state sequence, each element of the array represents a state, each state is represented as (a, b, c), which indicated that the left bank of a missionary The number of disabilities, b indicated that the number of the left bank of the Savage, c that ship is on the left bank, c = 1 for the shipping on the left bank, c = 0 for the boat on the right bank. If the problem is no solution, return only one element of " no solution"　of the array.