划分树

ACM模版

划分树

/* *  划分树(查询区间第k大)  */const int MAXN = 100010;int tree[20][MAXN];     //  表示每层每个位置的值int sorted[MAXN];       //  已经排序好的数int toleft[20][MAXN];   //  toleft[p][i]表示第i层从1到i有数分入左边void build(int l, int r, int dep){    if (l == r)    {        return;    }    int mid = (l + r) >> 1;    int same = mid - l + 1;         //  表示等于中间值而且被分入左边的个数    for (int i = l; i <= r; i++)    //  注意是l,不是one    {        if (tree[dep][i] < sorted[mid])        {            same--;        }    }    int lpos = l;    int rpos = mid + 1;    for (int i = l; i <= r; i++)    {        if (tree[dep][i] < sorted[mid])        {            tree[dep + 1][lpos++] = tree[dep][i];        }        else if (tree[dep][i] == sorted[mid] && same > 0)        {            tree[dep + 1][lpos++] = tree[dep][i];            same--;        }        else        {            tree[dep + 1][rpos++] = tree[dep][i];        }        toleft[dep][i] = toleft[dep][l - 1] + lpos - l;    }    build(l, mid, dep + 1);    build(mid + 1, r, dep + 1);    return ;}//  查询区间第k大的数,[L,R]是大区间,[l,r]是要查询的小区间int query(int L, int R, int l, int r, int dep, int k){    if(l == r)    {        return tree[dep][l];    }    int mid = (L + R) >> 1;    int cnt = toleft[dep][r] - toleft[dep][l - 1];    if (cnt >= k)    {        int newl = L + toleft[dep][l - 1] - toleft[dep][L - 1];        int newr = newl + cnt - 1;        return query(L, mid, newl, newr, dep + 1, k);    }    else    {        int newr = r + toleft[dep][R] - toleft[dep][r];        int newl = newr - (r - l - cnt);        return query(mid + 1, R, newl, newr, dep + 1, k - cnt);    }}int main(){    int n, m;    while (scanf("%d%d", &n, &m) == 2)    {        memset(tree, 0, sizeof(tree));        for (int i = 1; i <= n; i++)        {            scanf("%d", &tree[0][i]);            sorted[i] = tree[0][i];        }        sort(sorted + 1, sorted + n + 1);        build(1, n, 0);        int s, t, k;        while(m--)        {            scanf("%d%d%d", &s, &t, &k);            printf("%d\n", query(1, n, s, t, 0, k));        }    }    return 0;}