<script type="text/javascript">
    //<![CDATA[
    var rows = new Array(4)
    rows[0] = new Array (4)
    rows[1] = new Array (4)
    rows[2] = new Array (4)
    rows[3] = new Array (4)
    
    function checkWin() {
        var winner = false
        var checker = new Array(4)
        checker[0] = new Array (1, 2, 3, 4)
        checker[1] = new Array (5, 6, 7, 8)
        checker[2] = new Array (9, 10, 11, 12)
        checker[3] = new Array (13, 14, 15, 0)

        for (i = 0; i < 4; i++){
            for (j = 0; j < 4; j++){
                if (rows[i][j] == checker[i][j]){
                    winner = true
                }                    
            }
        }
        if (winner){
            alert("Congratulations! You've Won!")
            return true
        }
        return false
    }
                

    function move(tile){
        var obj = document.getElementById('tile' + tile)
        var win = false
        for (i = 0; i < 4; i++){
            for (j = 0; j < 4; j++){
                if (rows[i][j] == tile){
                    if (j > 0 && rows[i][j - 1] == 0){
                        obj.style.left = (j - 2) * 100 + 'px'
                        rows[i][j - 1] = tile
                        rows[i][j] = 0                        
                    }else if (j < 3 && rows[i][j + 1] == 0){
                        obj.style.left = (j + 2) * 100 + 'px'
                        rows[i][j + 1] = tile
                        rows[i][j] = 0
                    }else if (i > 0 && rows[i - 1][j] == 0){
                        obj.style.top = (i - 2) * 100 + 'px'
                        rows[i - 1][j] = tile
                        rows[i][j] = 0
                    }else if (i < 3 && rows[i + 1][j] == 0){
                        obj.style.top = (i + 2) * 100 + 'px'
                        rows[i + 1][j] = tile
                        rows[i][j] = 0
                    }
                    win = checkWin()
                    if (win){
                        break
                    }
                    return    
                }
            }
        }
                            
    }

    function initialize(){
        var check = new Array (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
        for (i = 0; i < 4; i++) {
            for (j = 0; j < 4; j++) {
                if (i == 3 && j == 3){
                                        rows[i][j] = 0
                                } else {
                    var n = Math.ceil(Math.random() * 15)
                    while (check[n - 1] == 0){
                        n = Math.ceil(Math.random() * 15)
                    }
                    rows[i][j] = n
                    check[n - 1] = 0
                    document.getElementById('tile' + n).style.left = (j + 1) * 100 + 'px'
                    document.getElementById('tile' + n).style.top = (i + 1) * 100 + 'px'
                }
            }
        }             
    }
    // ]]>
   </script>

alert("Sorry, Invalid Move");