js 二分法查找

例子：有序数组查找

//1递归做法

function findArr(arr,value,left,right){

var mid=Math.floor((left+right)/2);

//防止无穷递归

if(left>right){

return

}

if(arr[mid]>value){//左边

return findArr(arr,value,left,mid-1)

}else if(arr[mid]<value){//右边

return findArr(arr,value,mid+1,right)

}else{

return ‘找到了，位置是‘+mid;

}

};

//2 二进制做法

function binary(items,value,startIndex,stopIndex){

var middleIndex=(startIndex+stopIndex)>>>1;

while(items[middleIndex]!=value && startIndex<stopIndex){

if(items[middleIndex]>value){

stopIndex=middleIndex-1;

}else{

startIndex=middleIndex+1;

}

middleIndex=(startIndex+stopIndex)>>>1;

}

return items[middleIndex]!=value ? false:middleIndex;

}

var arr=[11,22,33,44,55,66,77,88,99];

alert(findArr(arr,66,0,arr.length-1));

alert(binary(arr,660,arr.length-1));