@VivianBalakrishnan's translation of Lee Hsien Loong's Sudoku solver.

vivian_balakrishnan_sudoku.js

/****************************************************************
 *	Sudoku Solver
 *
 *	Translated into Javascript from original code in C++
 *		by Lee Hsien Loong
 *	The MIT License (MIT)
 *	Copyright (c) 2015 Vivian Balakrishnan
 *
 *
 ****************************************************************/
BOARD_SIZE = 9; // Width and height of the SuDoku board
BOX_SIZE = 3; // Width and height of the inner boxes
EMPTY = ""; // Empty cell marker
BLANK = 0x0;
ONES = 0x3fe; //	Binary 1111111110
var InBlock = [];
var InRow = [];
var InCol = [];
var board = []; // Board of 81 cells

var Block = []; // 3x3 block of cells
var Row = []; // Row of 9 cells
var Col = []; // Column of 9 cells
var Seq = []; // Sequence of blank cells
var SeqPos = 0; // Points to blank cells



function nextfield(me) {
    var vnum = /[1-9]/;
    var elements = document.getElementsByTagName("input");
    for (i = 0; i < elements.length; i++) {

        if (elements[i] == me) {
            break;
        }
    }
    if (!elements[i].value.match(vnum)) {

        elements[i].value = "";
        elements[i].focus();
    } else {
        elements[i + 1].focus();

    }
}


function draw() {
    document.write('<table>');
    for (var row = 0; row < 9; row++) {
        document.write('<tr>');
        for (var col = 0; col < 9; col++) {
            document.write('<td><input type="text" size="1" maxlength="1" style="font-size:20px" onkeyup="nextfield(this)"/></td>');
        }
        document.write('</tr>');
    }
    document.write('</table>');
}


function setup() {
    board = document.getElementsByTagName("input");
    for (var i = 0; i < 81; i++) {
        var Square = i;
        InRow[Square] = (Math.floor(Square / BOARD_SIZE));
        InCol[Square] = (Square % BOARD_SIZE);
        InBlock[Square] = ((Math.floor(Square / 27)) * 3) + (Math.floor((Square % BOARD_SIZE) / 3));
    }

    for (var i = 0; i < 9; i++) {
        Block[i] = ONES;
        Row[i] = ONES;
        Col[i] = ONES;
    }

}

function bitcount(b) {
    b = b >>> 1;
    var count = 0;
    while (b) {
        b = (b >>> 1);
        count++;
    }
    return count;
}

function removeValbit(c, v) {
    Block[InBlock[c]] &= ~v;
    Row[InRow[c]] &= ~v;
    Col[InCol[c]] &= ~v;
}

function test(SeqNum) {

    if (SeqNum >= Seq.length) return true; //Solved

    var index = Seq[SeqNum];

    var possibles = Block[InBlock[index]] & Row[InRow[index]] & Col[InCol[index]];

    while (possibles) {

        var valbit = possibles & (-possibles);
        possibles &= ~valbit;

        board[index].value = bitcount(valbit);

        removeValbit(index, valbit);

        if (test(SeqNum + 1)) return true;

        Block[InBlock[index]] |= valbit;
        Row[InRow[index]] |= valbit;
        Col[InCol[index]] |= valbit;
    }
    return false;
}


function solve() {
    setup();
    for (var i = 0; i < 81; i++) {
        if (board[i].value != EMPTY) {
            var valbit2 = 1 << (board[i].value);
            removeValbit(i, valbit2);
        } else {
            Seq[Seq.length] = i;
        }
    }

    if (!test(0))
        alert("Cannot find solution");
}