360ship面试题

By | 2014/07/18

今天参加了360ship的网上面试,一共两道题,40分钟,感觉不算难,主要是算法问题,第一题问题如下:

A zero-indexed array A consisting of N integers is given. An equilibrium index of this array is any integer P such that 0 ≤ P < N and the sum of elements of lower indices is equal to the sum of elements of higher indices, i.e.

A[0] + A[1] + … + A[P−1] = A[P+1] + … + A[N−2] + A[N−1].

Sum of zero elements is assumed to be equal to 0. This can happen if P = 0 or if P = N−1.
For example, consider the following array A consisting of N = 7 elements:

A[0] = -7 A[1] = 1 A[2] = 5A[3] = 2 A[4] = -4 A[5] = 3A[6] = 0
P = 3 is an equilibrium index of this array, because:

* A[0] + A[1] + A[2] = A[4] + A[5] + A[6]

P = 6 is also an equilibrium index, because:

* A[0] + A[1] + A[2] + A[3] + A[4] + A[5] = 0

and there are no elements with indices greater than 6.
P = 7 is not an equilibrium index, because it does not fulfill the condition 0 ≤ P len(A)/2不成立,所以返回-1,如果A = [2,2,2,2,2,3,4,5,6],
num(2)>len(A)/2成立,所以返回2,代码如下:

def solution(A):
    dic = {}
    for i in A:
        if dic.has_key(i):
            dic[i] = dic.get(i) + 1
        else:
            dic.update({i: 1})
    l = dic.keys()
    for i in l:
        if dic[i]*2 > len(A):
            return i
    else:
        return -1

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