数据结构——划分树模板

http://www.notonlysuccess.com/index.php/divide-tree/

 

http://blog.sina.com.cn/s/blog_5f5353cc0100ki2e.html

 

以上为两个不错的讲解：

struct node{
    int l,r;
    int mid(){
        return (l + r)>>1;
    }
}tt[N<<2];

int toLeft[20][N];
int val[20][N],sorted[N];
int n,q;

void build(int l,int r,int rt,int d){
    int i;
    tt[rt].l = l;
    tt[rt].r = r;
    if (l == r) return ;
    int m = tt[rt].mid();
    int lsame = m - l + 1;//先假设做区间与m相等的放满
    //一一排除，保证左区间放的是<=sorted[m]的值
    for (i = l; i <= r; ++i){
        if (val[d][i] < sorted[m]) lsame--;
    }

    int lpos = l;
    int rpos = m + 1;
    int same = 0;

    for (i = l; i <= r; ++i){
        if (i == l) toLeft[d][i] = 0;
        else toLeft[d][i] = toLeft[d][i - 1];

        if (val[d][i] < sorted[m]){
            toLeft[d][i]++;
            val[d + 1][lpos++] = val[d][i];
        }
        else if (val[d][i] > sorted[m]){
            val[d + 1][rpos++] = val[d][i];
        }
        else{
            if (same < lsame){
                toLeft[d][i]++;
                val[d + 1][lpos++] = val[d][i];
                same++;
            }
            else{
                val[d + 1][rpos++] = val[d][i];
            }
        }
    }
    build(lc,d + 1);
    build(rc,d + 1);
}

int query(int L,int R,int k,int d,int rt){
   // printf("%d %d\n",L,R);
    if (L == R){
        return val[d][L];
    }
    int s = 0;
    int ss = 0;
    if (L == tt[rt].l){
        ss = 0;
        s = toLeft[d][R];
    }
    else{
        ss = toLeft[d][L - 1];
        s = toLeft[d][R] - toLeft[d][L - 1];
    }
    if (k <= s){
        int newl = tt[rt].l + ss;
        int newr = newl + s - 1;
        return query(newl,newr,k,d + 1,rt<<1);
    }
    else{
        int m = tt[rt].mid();
        int bb = L - tt[rt].l - ss;
        int b = R - L + 1 - s;
        int newl = m + bb + 1;
        int newr = newl + b - 1;
        return query(newl,newr,k - s,d + 1,rt<<1|1);
    }
}