validMountainArray.js

/**
 * @param {number[]} A
 * @return {boolean}
 */
var validMountainArray = function(A) {
    if (A.length < 3) {
        return false;
    }
    let current = A[0];
    let i = 1;
    while (current < A[i] && i < A.length) {
        current = A[i];
        i++;
    }
    
    if (i == 1 || i >= A.length) {
        return false;
    }
    while (current > A[i] && i < A.length) {
        current = A[i];
        i++;
    }
    
    if (i < A.length) {
        return false;
    } else {
        return true;
    }
    
};