function getCells(s) {

    // Split the input string by ':' to get the starting and ending cells

    let [start, end] = s.split(':');

    // Get the column numbers of the starting and ending cells

    let startCol = getColNum(start[0]);

    let endCol = getColNum(end[0]);

    // Get the row numbers of the starting and ending cells

    let startRow = parseInt(start.substring(1));

    let endRow = parseInt(end.substring(1));

    // Initialize an empty array to store the cells

    let cells = [];

    // Loop through the columns

    for (let col = startCol; col <= endCol; col++) {

        // Loop through the rows

        for (let row = startRow; row <= endRow; row++) {

            // Get the column letter and concatenate it with the row number

            let colLetter = getColLetter(col);

            let cell = colLetter + row;

            // Add the cell to the array

            cells.push(cell);

        }

    }

    // Sort the cells in non-decreasing order by columns and then by rows

    cells.sort((a, b) => {

        if (a[0] === b[0]) {

            // If the columns are the same, sort by the row numbers

            return parseInt(a.substring(1)) - parseInt(b.substring(1));

        } else {

            // If the columns are different, sort by the column letters

            return a[0].charCodeAt(0) - b[0].charCodeAt(0);

        }

    });

    return cells;

}

​

// Function to get the column number given a column letter

function getColNum(colLetter) {

    // Initialize the column number to 0

    let colNum = 0;

    // Loop through the column letter

    for (let i = 0; i < colLetter.length; i++) {

        // Increment the column number by 26 for each letter in the column letter

        colNum = colNum * 26 + (colLetter.charCodeAt(i) - 'A'.charCodeAt(0) + 1);

    }

    return colNum;

}

​

// Function to get the column letter given a column number

function getColLetter(colNum) {

    // Initialize the column letter to an empty string

    let colLetter = '';

    // Loop until the column number is greater than 0

    while (colNum > 0) {

        // Get the remainder when the column number is divided by 26

        let remainder = (colNum - 1) % 26;

        // Add the letter corresponding to the remainder to the beginning of the column letter

        colLetter = String.fromCharCode(remainder + 'A'.charCodeAt(0)) + colLetter;

        // Divide the column number by 26 and round down to the nearest integer

        colNum = Math.floor((colNum - 1) / 26);

    }

    return colLetter;

}

​