JS数组的二分查找算法

用途：对有序数组进行查找。如：查找指定元素在数组中的下标

/*
@param {number} target 查找的目标值
@param {array} arr 被查找的数组
@return {number} target所在的数组下标位置
*/
function binarySearch(target,arr) {
    var start   = 0;
    var end     = arr.length-1;

    while (start<=end){
        var mid = parseInt(start+(end-start)/2);
        if(target==arr[mid]){
            return mid;
        }else if(target>arr[mid]){
            start   = mid+1;
        }else{
            end     = mid-1;
        }
    }
    return -1;
}
//递归写法（和上面一样，只是拆成了递归）
function binarySearch(target,arr,start,end) {
    var start   = start || 0;
    var end     = end || arr.length-1;

    var mid = parseInt(start+(end-start)/2);
    if(target==arr[mid]){
        return mid;
    }else if(target>arr[mid]){
        return binarySearch(target,arr,mid+1,end);
    }else{
        return binarySearch(target,arr,start,mid-1);
    }
    return -1;
}