//查找第一次出现的位置
int search(int a[], int t){
    int r = n - 1, l = 0;
    //cout << r << " " << l << "--" << mid << endl;

    while(l < r){
        int mid = l + r >> 1;
        if (a[mid] >= t) r = mid;
        else l = mid + 1;
    }
    return l;
}