896.monotonic-array.cpp

/*
 * @lc app=leetcode id=896 lang=cpp
 *
 * [896] Monotonic Array
 *
 * https://leetcode.com/problems/monotonic-array/description/
 *
 * algorithms
 * Easy (54.56%)
 * Total Accepted:    24.1K
 * Total Submissions: 44.2K
 * Testcase Example:  '[1,2,2,3]'
 *
 * 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 Solution {
public:
    bool isMonotonic(vector<int>& A) {
        int N = A.size();
        if(N < 2)
            return true;
        if(A[0]<=A[N-1]){ // must be increasing
            for(int i=0;i<N-1;i++){
                if(A[i] > A[i+1])
                    return false;
            }
        }else{ // must be decreasing
            for(int i=0;i<N-1;i++){
                if(A[i] < A[i+1])
                    return false;
            }
        }
        return true;
    }
};