Two Pointers

From beginn side and end site to loop. JS and PY3

let fn = arr => {
    let left = 0, ans = 0, right = arr.length - 1;

    while (left < right) {
        // coding here for what is required!
        if (CONDITION) {
            left++;
        } else {
            right--;
        }
    }

    return ans;
}

def fn(arr):
    left = ans = 0
    right = len(arr) - 1

    while left < right:
        ## coding here for what is required!
        if CONDITION:
            left += 1
        else:
            right -= 1
    
    return ans

If there are two arrays, run with following template

let fn = (arr1, arr2) => {
    let i = 0, j = 0, ans = 0;
    
    while (i < arr1.length && j < arr2.length) {
        // coding here for what is required!
        if (CONDITION) {
            i++;
        } else {
            j++;
        }
    }

    while (i < arr1.length) {
        // coding here for what is required!
        i++;
    }

    while (j < arr2.length) {
        // coding here for what is required!
        j++;
    }

    return ans;
}