【劍指offer】16—把數組排成最小的數

輸入一個正整數數組，把數組裏所有數字拼接起來排成一個數，打印能拼接出的所有數字中最小的一個。例如輸入數組{3，32，321}，則打印出這三個數字能排成的最小數字爲321323。

方法一：利用內置函數實現全排列，然後找出最小值

class Solution:
    def PrintMinNumber(self, numbers):
        # write code here
        if not numbers:
            return ""
        import itertools
        A = list(itertools.permutations(numbers))

        result = []

        for each in A:
            min_str =''
            for j in each:
                min_str += str(j)
            result.append(int(min_str))
        print(result)
        return min(result)

方法二，利用回溯法實現全排列，然後找出最小值

class Solution1:
    def PrintMinNumber(self, numbers):

        if not numbers:
            return ""
        res =[]
        def backtree(numbers,tmp):

            if not numbers:
                res.append(tmp)
                return
            for i in range(len(numbers)):
                backtree(numbers[:i]+numbers[i+1:],tmp+[numbers[i]])
        backtree(numbers,[])
        # 對於排列好的數字尋找最小值
        result = []
        for i in res:
            s = ''
            for j in i:
                s += str(j)
            result.append(int(s))
        print(result)
        return min(result)

print(Solution1().PrintMinNumber([3,5,1,4,2]))