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March 4, 2011 17:33
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javascript master class with Amy Hoy and Thomas Fuchs: Homework part 1
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// Part 1. | |
// Implement a function prototype extension that caches function results for | |
// the same input arguments of a function with one parameter. | |
// | |
// For example: | |
// Make sin(1) have the result of Math.sin(1), but use a cached value | |
// for future calls. | |
// | |
// Part 2. | |
// Use this new function to refactor the code example. | |
// Some good test numbers: 524287, 9369319, 2147483647 (all primes) | |
Function.prototype.cached = function( num, method ){ | |
if( this.cache == null ){ | |
this.cache = {}; | |
} | |
if( this.cache[ num ] != null ){ | |
return this.cache[ num ]; | |
}else{ | |
var result = method( num ); | |
this.cache[ num ] = result + '(cache hit)'; | |
return result; | |
} | |
} | |
function cachedSin( num ) { | |
return cachedSin.cached( num, function( num ){ | |
// everything but 1 can be prime | |
var sin = Math.sin(num); | |
return sin; | |
}); | |
}; | |
function isPrime( num ) { | |
return isPrime.cached( num, function( num ){ | |
// everything but 1 can be prime | |
var prime = num != 1; | |
for ( var i = 2; i < num; i++ ) { | |
if ( num % i == 0 ) { | |
prime = false; | |
break; | |
} | |
} | |
return prime; | |
}); | |
}; | |
console.log( isPrime(524287) ); | |
console.log( isPrime(524287) ); | |
console.log( cachedSin(1) ); | |
console.log( cachedSin(1) ); |
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