参考：
https://www.cnblogs.com/grandyang/p/10961560.html
#include <vector>
#include <stdlib.h>
#include <ostream>
#include <string>
using namespace std;
/**
* @brief The Solution1 class
* 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
*/
class Solution1{
public:
bool isMonotonic(vector<int>& A){
bool inc = true, dec = true;
for(int i = 1; i < A.size(); ++i){
inc &= (A[i-1] <= A[i]);
dec &= (A[i-1] >= A[i]);
if(!inc && !dec) return false;
}
return true;
}
};
class Solution2{
public:
bool isMonotonic(vector<int>&A){
int inc = 1,dec = 1,n = A.size();
for(int i = 1; i < n; ++i){
inc += (A[i-1] <= A[i]);
dec += (A[i-1] >= A[i]);
}
return (inc == n) || (dec == n);
}
};