另一种fib高效实现

var memoize = function(fn) {
  var cache = [];
  return function(i) {
    return (i in cache) ? cache[i] :
      (cache[i] = fn.call(arguments.callee, i));
  };
}
 
var fib = new memoize(function(i) {
  if (i == 0 || i == 1)
    return 1;
  return this(i-1) + this(i-2);
})

<!doctype html>
<html>
  <head>
    <title>缓存函数形式的fib</title>
    <style>
      table {
        border-collapse: collapse;
        width:100%;
      }
      table td {
        border: 1px solid firebrick;
      }

</style>
    <script>

var memoize = function(fn) {
        var cache = [];
        return function(i) {
          return (i in cache) ? cache[i] :
            (cache[i] = fn.call(arguments.callee, i));
        };
      }

var fib = new memoize(function(i) {
        if (i == 0 || i == 1)
          return 1;
        return this(i-1) + this(i-2);
      });

var draw = function(){
        
        var table = ["<table>"]
        function test(n) {
          var t = new Date;
          for (var i = 0; i < 1000; i++) {
            var res = fib(n);
          }
          t = new Date - t;
          table.push('<tr><td>',n,'</td><td>',res,'</td><td>',t,'</td><td>',(t/n).toFixed(2) ,'</td></tr>');
        }

for (var i = 0; i < 79; i++) {
          test(i);
        }
        table.push('</table>');
        var div = document.createElement('div');
        div.innerHTML = table.join('');
        document.body.appendChild(div);
        
      }

</script>
  </head>
  <body onload="draw();">

</body>
</html>

新的实现：

function fib(n) {
  function _fib(n, a, b, arg1, arg2) {
    if(n>1) _fib(n-1, a, b, arguments, arg1);
    return arg1[2] = arg2[1] = a+b;
  }

  return _fib(n, 0, 1, [], []);
}

<!doctype html>
<html>
  <head>
    <title>用arguments递归形式实现的fib</title>
    <style>
      table {
        border-collapse: collapse;
        width:100%;
      }
      table td {
        border: 1px solid firebrick;
      }

</style>
    <script>

function fib(n) {
        function _fib(n, a, b, arg1, arg2) {
          if(n>1) _fib(n-1, a, b, arguments, arg1);
          return arg1[2] = arg2[1] = a+b;
        }
        return _fib(n, 0, 1, [], []);
      }

</script>
  </head>
  <body onload="draw();">

</body>
</html>

posted on 2010-09-19 09:14 司徒正美阅读(1259) 评论(3) 编辑收藏举报

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另一种fib高效实现