Monotonic Array Check

Definition

An array is monotonic if it is either:

• Non-decreasing (each element is greater than or equal to the previous one), or
• Non-increasing (each element is less than or equal to the previous one)..

Single-element arrays are always monotonic.

Function Purpose

The checkMonotonic function checks whether a given array follows a monotonic order.

const checkMonotonic = function (array){
    const first = array[0];
    const last = array[array.length-1];
// 1.......10
    if(first === last){
        for(let i=0;i<array.length-1;i++){
            if(array[i+1]!==array[i]) return false;
        }
    }
    else if (first<last){
        // non decreasing
        for(let i=0;i<array.length-1;i++){
            if(array[i+1]<array[i]) return false;
        }
    }
    else{
        // non increasing
        for(let i=0;i<array.length-1;i++){
            if(array[i+1]>array[i]) return false;
        } 
    }
    return true;
}

checkMonotonic([9]);

How It Works

1. Identify Direction
   • Compare the first and last elements of the array.
   • This determines whether the array should be:
     • Constant
     • Increasing (non-decreasing)
     • Decreasing (non-increasing)
2. Validate Order
   • Traverse the array once.
   • At each step, compare the current element with the next one.
   • If the expected order is violated, return false.
3. Return Result
   • If no violations are found, return true.