【算法】二分查找

template <typename T>
int binarySearch(T arr[],int n, T targrt){
    int l = 0, r = n-1;  // arr[l ...  r]
    while(l <= r){
        //int mid = (l+r)/2;
        int mid = l + (r-l)/2;
        if(arr[mid] == targrt) return mid;
        if(targrt < arr[mid]) r = mid - 1;
        else l = mid + 1;
    }
    return -1;
}

时间复杂度O(log(n));