权值树状数组求第k大/小数

int kth(int k){
	int sum = 0,x = 0;
	for(int i = lg[n];i >= 0;-- i){
		int y = x + (1<<i);
		if(y < m && sum + tr[y] < k){
			x = y;
			sum += tr[y];
		}
	}
	return x+1;
}