57. 和为s的数字

双指针
注意要返回[],返回None会出错

class Solution:
    def FindNumbersWithSum(self, array, tsum):
        # write code here
        if not array :
            return []
        first = 0
        lenth = len(array) - 1
        last = lenth
        while last > first:
            if array[first] + array[last] > tsum:
                last -= 1
            elif array[first] + array[last] < tsum:
                first += 1
            elif array[first] + array[last] == tsum:
                return [array[first],array[last]]
        return []