shiawuen/index.html

## index.html
<!DOCTYPE HTML>
<html lang="en-US">
<head>
  <meta charset="UTF-8">
  <title>Combination – slooow way</title>
</head>
<body>

  <script src="index.js"></script>
</body>
</html>

## index.js
/*
  Given a number n, generate all possible sequences of numbers that add up to n, where the numbers in the
  sequence are in non-ascending order.
  e.g., n=4, then
    4
    3,1
    2,2
    2,1,1
    1,1,1,1
*/
(function() {

var n = 20;
var slice = Array.prototype.slice;
var prev = +new Date();
var count = 0;


compute(n);


function compute(set, variable) {
  if (!Array.isArray(set)) {
    set = [set];
    variable = 0;
  }

  var sLen = set.length;

  if (variable <= set[sLen-1]) {
    var result = set.join(',');

    if (variable)
      result += ',' + variable;

    count += 1;
    console.log(result);
  }


  // Terminate the loop when all value == 1
  if (set[0] === 1 && variable === 1) {
    console.log('Total time spent: ' + (+new Date() - prev) + 'ms');
    console.log(count + ' combinations generated')
    return;
  }


  var s = set[sLen-1]
    , newSet
    , nsLen
    , vSet
    , index;

  if (s < variable) {
    set.push(s);
    variable -= s;

    setTimeout(function() {
      compute(set, variable);
    }, 1);

    return;
  }


  newSet = slice.call(set);

  if (s === variable && s !== 1) {
    newSet.push(s)
    variable = 0;
  } else if (s-variable < 1) {
    index = indexOfBefore(set, 1);

    newSet = slice.call(set, 0, index+1);
    vSet = slice.call(set, index+1, sLen);

    for (var vl = vSet.length; vl;) {
      variable += vSet[--vl];
    }
  }

  nsLen = newSet.length;
  newSet[nsLen-1] -= 1;
  variable += 1;

  if (variable > newSet[nsLen-1]) {
    newSet.push(newSet[nsLen-1]);
    variable = variable - newSet[nsLen-1];
  } else if (variable > 1) {
    newSet.push(variable);
    variable = 0;
  }

  // Hack to prevent the maximum stack call error
  setTimeout(function() {
    compute(newSet, variable);
  }, 1);
}


function indexOfBefore(set, v) {
  var index = set.indexOf(v);
  return index === -1
    ? set.length-1
    : index !== 0
      ? index-1 // The one before the first item with value=v
      : -1; // all value are same
}

})();
	<!DOCTYPE HTML>
	<html lang="en-US">
	<head>
	<meta charset="UTF-8">
	<title>Combination – slooow way</title>
	</head>
	<body>

	<script src="index.js"></script>
	</body>
	</html>
	/*
	Given a number n, generate all possible sequences of numbers that add up to n, where the numbers in the
	sequence are in non-ascending order.
	e.g., n=4, then
	4
	3,1
	2,2
	2,1,1
	1,1,1,1
	*/
	(function() {

	var n = 20;
	var slice = Array.prototype.slice;
	var prev = +new Date();
	var count = 0;


	compute(n);


	function compute(set, variable) {
	if (!Array.isArray(set)) {
	set = [set];
	variable = 0;
	}

	var sLen = set.length;

	if (variable <= set[sLen-1]) {
	var result = set.join(',');

	if (variable)
	result += ',' + variable;

	count += 1;
	console.log(result);
	}


	// Terminate the loop when all value == 1
	if (set[0] === 1 && variable === 1) {
	console.log('Total time spent: ' + (+new Date() - prev) + 'ms');
	console.log(count + ' combinations generated')
	return;
	}


	var s = set[sLen-1]
	, newSet
	, nsLen
	, vSet
	, index;

	if (s < variable) {
	set.push(s);
	variable -= s;

	setTimeout(function() {
	compute(set, variable);
	}, 1);

	return;
	}


	newSet = slice.call(set);

	if (s === variable && s !== 1) {
	newSet.push(s)
	variable = 0;
	} else if (s-variable < 1) {
	index = indexOfBefore(set, 1);

	newSet = slice.call(set, 0, index+1);
	vSet = slice.call(set, index+1, sLen);

	for (var vl = vSet.length; vl;) {
	variable += vSet[--vl];
	}
	}

	nsLen = newSet.length;
	newSet[nsLen-1] -= 1;
	variable += 1;

	if (variable > newSet[nsLen-1]) {
	newSet.push(newSet[nsLen-1]);
	variable = variable - newSet[nsLen-1];
	} else if (variable > 1) {
	newSet.push(variable);
	variable = 0;
	}

	// Hack to prevent the maximum stack call error
	setTimeout(function() {
	compute(newSet, variable);
	}, 1);
	}


	function indexOfBefore(set, v) {
	var index = set.indexOf(v);
	return index === -1
	? set.length-1
	: index !== 0
	? index-1 // The one before the first item with value=v
	: -1; // all value are same
	}

	})();