【题目】
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.
Example 1:
Input: [1,2,2,3]
Output: true
Example 2:
Input: [6,5,4,4]
Output: true
Example 3:
Input: [1,3,2]
Output: false
Example 4:
Input: [1,2,4,5]
Output: true
Example 5:
Input: [1,1,1]
Output: true
Note:
1 <= A.length <= 50000-100000 <= A[i] <= 100000【题意】
判断是否是单调数组。
【解答】
用两个bool变量分别记录是否出现neg差值和pos差值，单调数组的话，两个不可能同时为true。
时间O(N) 空间O(1)
class Solution { public: bool isMonotonic(vector<int>& A) { int len = A.size(); bool isNeg = false; bool isPos = false; for(int i=0; i+1<len; i++){ int diff = A[i+1] - A[i]; if(diff < 0){ isNeg = true; if(isPos) return false; } if(diff > 0){ isPos = true; if(isNeg) return false; } } return true; } };
原文：https://www.cnblogs.com/xxinn/p/10310650.html