Created
January 11, 2012 05:11
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| <!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> |
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| /* | |
| 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 | |
| } | |
| })(); |
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recursion?