Solution

• Solution is time unefficient, but memorywise beats 100%.

function isValidSudoku(board: string[][]): boolean {
    for(let i = 0; i < 9; i++){
        if(checkIsValid(board[i]) !== true){
            return false
        }
        const verticalRow = []
        for(let k = 0; k < 9; k++){
            verticalRow.push(board[k][i])
        }
        if(checkIsValid(verticalRow) !== true){
            return false
        }
        if(checkIsValid(getSuBox(board, i)) !== true){
            return false
        }
    }
    return true
};

function checkIsValid(cells: string[]): boolean {
    const filled = cells.filter(cell => cell !== ".")
    return (new Set(filled)).size === filled.length
}

function getSuBox(board: string[][], index: number): string[] {
    const ranges = {
        0: [0,1,2],
        1: [3,4,5],
        2: [6,7,8],
    }
    
    const hRange = ranges[index % 3];
    const vRange = ranges[Math.floor((index)/3)]

    return [
        board[hRange[0]][vRange[0]],
        board[hRange[1]][vRange[0]],
        board[hRange[2]][vRange[0]],
        board[hRange[0]][vRange[1]],
        board[hRange[1]][vRange[1]],
        board[hRange[2]][vRange[1]],
        board[hRange[0]][vRange[2]],
        board[hRange[1]][vRange[2]],
        board[hRange[2]][vRange[2]],
    ]
}