896. Monotonic Array@python

An array is monotonic if it is either monotone increasing or monotone decreasing.

An array A is monotone increasing if for all i <= j, A[i] <= A[j].  An array A is monotone decreasing if for all i <= j, A[i] >= A[j].

Return true if and only if the given array A is monotonic.

原题:leetcode 896.Monotonic Array

题意:判断一个数组是否是单调的

1.判断单调性:数组值比较

存在三种情况:

(1)A[0] > A[-1]: 单调递减

(2)A[0] < A[-1]: 单调递增

(3)A[0] == A[-1]: 所有值全相等

2.遍历数组,验证数组是否单调递增或者单调递减或者不变

代码如下:

class Solution(object):
    def isMonotonic(self, A):
        """
        :type A: List[int]
        :rtype: bool
        """
        n = len(A)
        i = 0
        if A[0] < A[n-1]:   # 单调递增
            while i < n-1:
                if A[i] <= A[i+1]:
                    i += 1
                else:
                    return False
            return True
        elif A[0] > A[n-1]:  # 单调递减
            while i < n-1:
                if A[i] >= A[i+1]:
                    i += 1
                else:
                    return False
            return True
        else:                     # 不变
            while i < n-1:
                if A[i] == A[i+1]:
                    i += 1
                else:
                    return False
            return True

时间复杂度: O(n)

空间复杂度: O(1)