monotonic-array problem L896

3sum problem

3sum leetcode

solution

class Solution {
    public boolean isMonotonic(int[] nums) {

		if (nums.length <= 2) return true;
		var direction = nums[1] - nums[0];
		for (int i = 2; i < nums.length; i++) {
			if (direction == 0) {
				direction = nums[i] - nums[i-1];
				continue;
			}
			var difference = nums[i] - nums[i-1];
			if (direction > 0){
				if(difference < 0){
					return false;
				} 
			} else {
				if(difference > 0) {
					return false;	
				}
			}
		}
        return true;
    }
}

For this problem,

we can loop through the array while keeping thrack of the difference. If the direction changes, we can return false.

Another solution we can make is the following

class Solution {
    public boolean isMonotonic(int[] nums) {

		var isNonDecreasing = true;
		var isNonIncreasing = true;
		for (int i=1;i<nums.length;i++){
			if(nums[i] < nums[i-1]){
				isNonDecreasing = false; 
			}
			if(nums[i] > nums[i-1]){
				isNonIncreasing = false;
			}
		}
    return isNonDecreasing || isNonIncreasing;
    }
}

Both of the solution has a complexity of O(n) time | O(1) space