折半查找

function binarySearch(array,x){
  var lowPoint=1;                    
 var higPoint=array.length;
 var returnValue=-1;               
 var midPoint;
 var found=false;                  
 while ((lowPoint<=higPoint)&&(!found)){
  midPoint=Math.ceil((lowPoint+higPoint)/2);
  //console.log(lowPoint+"===="+midPoint+"===="+higPoint);
  if(x>array[midPoint-1]){
   lowPoint=midPoint+1;
  }
  else if(x<array[midPoint-1]){
   higPoint= midPoint-1;
  }
  else if(x=array[midPoint-1]){
   found=true;
  }

 }
 if(found){
    returnValue=midPoint;
 }
 return returnValue;
}
/*var array2=[1,2,3,4,5,6,7,8,9,100,109];*/
var array2=['a','b','c','d','e','f','g'];
console.log(binarySearch(array2,'c'));