Suffix Array

Suffix Array (接尾辞配列)
* 関連： http://en.wikipedia.org/wiki/Suffix_array
* http://rest-term.com/archives/2791/

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license : MIT License
modified : 2010-05-16 23:03:03

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/**
 * Suffix Array (接尾辞配列)
 * 関連： http://en.wikipedia.org/wiki/Suffix_array
 *       http://rest-term.com/archives/2791/
 */
package {
  import flash.display.Sprite;
  import flash.text.TextField;
    
  public class Main extends Sprite {
    private var sa:SuffixArray;
    private var tf:TextField;
    
    public function Main() {
      sa = new SuffixArray();
      tf = new TextField();
      tf.width = 400;
      tf.height = 400;
      addChild(tf);
      var source:String = "wonderfl";
      var target:String = "fl";
      sa.addEventListener(SuffixArray.BUILD_COMPLETE, function():void {
        tf.text = "Source String: " + source +
          "\n----- Suffix Array -----\n";
        tf.appendText(sa.toString());
        tf.appendText("\n------------------------\n" + 
          "Target Substring: " + target +
          "\nIndex: " + sa.search(target).toString());
      }, false, 0, true);
      sa.build(source);
    }
  }
}
 
 
import __AS3__.vec.Vector;
import flash.events.Event;
import flash.events.EventDispatcher;
import flash.utils.getTimer;
  
class SuffixArray extends EventDispatcher {  
  public static const BUILD_COMPLETE:String = "build_complete";
  private var suffixes:Vector.<String>;
  private var len:int;
  private var _time:Number;
  
  public override function toString():String {
    return suffixes.join("\n");
  }
  /**
   * search substring, using binary search O(mlogn)
   */
  public function search(substring:String):int {
    if(len == 0) return substring.length == 0 ? 0 : -1;
    var low:int = 0, high:int = suffixes.length - 1;
    while(low < high) {
      var middle:int = low + (high - low)/2;
      if(suffixes[middle] >= substring) high = middle;
      else low = middle + 1;
    }
    if(suffixes[high].indexOf(substring, 0) == 0) {
      return len - suffixes[high].length;
    }
    return -1;
  }
  /**
   * build Suffix Array, O(n^2logn)
   */
  public function build(str:String):void {
    _time = getTimer();
    len = str.length;
    suffixes = new Vector.<String>(len, true);
    for(var i:int = 0; i < len; i++) {
      suffixes[i] = str.substring(i);
    }
    suffixes.sort(
      function(x:String, y:String):int {
        return x > y ? 1 : x < y ? -1 : 0;
      }
    );
    _time = getTimer() - _time;
    dispatchEvent(new Event(BUILD_COMPLETE));
  }
  public function get time():Number {
    return _time;
  }
}

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