[数据结构]二分查找

1，二分查找：

点击打开链接

 

int Find(int arr[], int key,int length)
{
 assert(arr!=NULL&&length>0);
int low=0,high=length,mid;
while(low<=high)
 {
 mid=(low+high)/2;
if(arr[mid]==key) return mid;
else
 {
if(arr[mid]>key) high=mid-1;
else low=mid+1;
 }
 }
return-1;
}

假定集合中油重复的元素，找到某个数首次出现的位置

 

 

int find(int * arr , int length, int key){
    int low = 0,high = length-1,mid;
    while(low <= high){
        mid = (low + high)/2;
        if (arr[mid] < key){
            low = mid + 1;
        }else if(arr[mid] > key){
            high = mid - 1;
        }else{
            if (mid == 0) return mid;
            if (mid >= 1 && arr[mid-1] != key) return mid;
            else high = mid - 1;
        }
    }
    return -1;
}