acwing算法提高之数据结构--平衡树Treap

1 介绍

本博客用来记录使用平衡树求解的题目。

插入、删除、查询操作的时间复杂度都是O(logN)。

动态维护一个有序序列。

2 训练

题目1：253普通平衡树

C++代码如下，

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>

using namespace std;

const int N = 100010, INF = 1e8;

int n;
struct Node {
    int l, r;
    int key, val;
    int cnt, size;
}tr[N];

int root, idx;

void pushup(int p) {
    tr[p].size = tr[tr[p].l].size + tr[tr[p].r].size + tr[p].cnt;
}

int get_node(int key) {
    tr[++idx].key = key;
    tr[idx].val = rand();
    tr[idx].cnt = tr[idx].size = 1;
    return idx;
}

void zig(int &p) {
    int q = tr[p].l;
    tr[p].l = tr[q].r, tr[q].r = p, p = q;
    pushup(tr[p].r), pushup(p);
}

void zag(int &p) {
    int q = tr[p].r;
    tr[p].r = tr[q].l, tr[q].l = p, p = q;
    pushup(tr[p].l), pushup(p);
}

void build() {
    get_node(-INF), get_node(INF);
    root = 1, tr[1].r = 2;
    pushup(root);
    
    if (tr[1].val < tr[2].val) zag(root);
}

void insert(int &p, int key) {
    if (!p) p = get_node(key);
    else if (tr[p].key == key) tr[p].cnt++;
    else if (tr[p].key > key) {
        insert(tr[p].l, key);
        if (tr[tr[p].l].val > tr[p].val) zig(p);
    } else {
        insert(tr[p].r, key);
        if (tr[tr[p].r].val > tr[p].val) zag(p);
    }
    pushup(p);
}

void remove(int &p, int key) {
    if (!p) return;
    if (tr[p].key == key) {
        if (tr[p].cnt > 1) tr[p].cnt --;
        else if (tr[p].l || tr[p].r) {
            if (!tr[p].r || tr[tr[p].l].val > tr[tr[p].r].val) {
                zig(p);
                remove(tr[p].r, key);
            } else {
                zag(p);
                remove(tr[p].l, key);
            }
        } else {
            p = 0;
        }
    } else if (tr[p].key > key) remove(tr[p].l, key);
    else remove(tr[p].r, key);
    
    pushup(p);
}

int get_rank_by_key(int p, int key) {
    if (!p) return 0;
    if (tr[p].key == key) return tr[tr[p].l].size + 1;
    if (tr[p].key > key) return get_rank_by_key(tr[p].l, key);
    return tr[tr[p].l].size + tr[p].cnt + get_rank_by_key(tr[p].r, key);
}

int get_key_by_rank(int p, int rank) {
    if (!p) return INF;
    if (tr[tr[p].l].size >= rank) return get_key_by_rank(tr[p].l, rank);
    if (tr[tr[p].l].size + tr[p].cnt >= rank) return tr[p].key;
    return get_key_by_rank(tr[p].r, rank - tr[tr[p].l].size - tr[p].cnt);
}

int get_prev(int p, int key) {
    if (!p) return -INF;
    if (tr[p].key >= key) return get_prev(tr[p].l, key);
    return max(tr[p].key, get_prev(tr[p].r, key));
}

int get_next(int p, int key) {
    if (!p) return INF;
    if (tr[p].key <= key) return get_next(tr[p].r, key);
    return min(tr[p].key, get_next(tr[p].l, key));
}

int main() {
    build();
    scanf("%d", &n);
    
    while (n--) {
        int opt, x;
        scanf("%d%d", &opt, &x);
        
        if (opt == 1) insert(root, x);
        else if (opt == 2) remove(root, x);
        else if (opt == 3) printf("%d\n", get_rank_by_key(root, x) - 1);
        else if (opt == 4) printf("%d\n", get_key_by_rank(root, x + 1));
        else if (opt == 5) printf("%d\n", get_prev(root, x));
        else printf("%d\n", get_next(root, x));        
    }
    
    return 0;
}
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使用C++的multiset，超时了，通过了 6/11个数据

#include <iostream>
#include <cstring>
#include <algorithm>
#include <set>

using namespace std;

int main() {
    multiset<int> s;
    int m;
    cin >> m;
    while (m--) {
        int op, x;
        cin >> op >> x;
        
        if (op == 1) {
            s.insert(x);
        } else if (op == 2) {
            s.extract(x);
        } else if (op == 3) {
            int idx = distance(s.begin(), s.lower_bound(x));
            cout << 1 + idx << endl;
        } else if (op == 4) {
            x -= 1; //下标从0开始
            auto it = s.begin();
            advance(it, x);
            cout << *it << endl;
        } else if (op == 5) {
            auto it = s.lower_bound(x);
            it--; //保证一定有解
            cout << *it << endl;
        } else if (op == 6) {
            auto it = s.upper_bound(x);
            cout << *it << endl;
        }
    }
    return 0;
}
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使用python3的库sortedcontainers，发现acwing报错没有该模块，

from sortedcontainers import SortedList
import bisect

sl = SortedList()

m = int(input())
for i in range(m):
    line = intput()
    
    ls_line = line.split()
    ls_line = [int(x) for x in ls_line]
    op = ls_line[0]
    x = ls_line[1]
    
    if op == 1:
        sl.add(x)
    elif op == 2:
        sl.remove(x)
    elif op == 3:
        i = bisect.bisect_left(sl, x)
        print(i + 1)
    elif op == 4:
        print(sl[x-1])
    elif op == 5:
        it = bisect.bisect_left(ls, x)
        it -= 1
        print(sl[it])
    elif op == 6:
        it = biset.bisect_right(ls, x)
        print(sl[it])
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题目2：265营业额统计

使用C++的multiset，

#include <iostream>
#include <cstring>
#include <algorithm>
#include <set>
#include <climits>

using namespace std;

int main() {
    int n;
    cin >> n;
    
    long long res = 0;
    multiset<int> s;
    for (int i = 0; i < n; ++i) {
        int t;
        cin >> t;
        
        if (i == 0) {
            res += t;
            
            s.insert(t); //插入数t
            
            continue;
        }
        
        int ans = 0x3f3f3f3f;
        //求大于等于t的迭代器
        auto iter1 = s.lower_bound(t);
        if (iter1 != s.end()) {
            int x = *iter1;
            ans = min(ans, abs(x - t));
        }
        
        if (iter1 != s.begin()) {
            auto iter2 = iter1;
            iter2--;
            int x = *iter2;
            ans = min(ans, abs(x - t));
        }
        
        res += ans;
        
        s.insert(t); //插入数t
    }
    cout << res << endl;
    
    return 0;
}
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C++代码如下，

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>

using namespace std;

typedef long long LL;

const int N = 33010, INF = 1e7;

int n;
struct Node {
    int l, r;
    int key, val;
}tr[N];

int root, idx;

int get_node(int key) {
    tr[++idx].key = key;
    tr[idx].val = rand();
    return idx;
}

void build() {
    get_node(-INF), get_node(INF);
    root = 1, tr[1].r = 2;
}

void zig(int &p) {
    int q = tr[p].l;
    tr[p].l = tr[q].r, tr[q].r = p, p = q;
}

void zag(int &p) {
    int q = tr[p].r;
    tr[p].r = tr[q].l, tr[q].l = p, p = q;
}

void insert(int &p, int key) {
    if (!p) p = get_node(key);
    else if (tr[p].key == key) return;
    else if (tr[p].key > key) {
        insert(tr[p].l, key);
        if (tr[tr[p].l].val > tr[p].val) zig(p);
    } else {
        insert(tr[p].r, key);
        if (tr[tr[p].r].val > tr[p].val) zag(p);
    }
}

int get_prev(int p, int key) {
    if (!p) return -INF;
    if (tr[p].key > key) return get_prev(tr[p].l, key);
    return max(tr[p].key, get_prev(tr[p].r, key));
}

int get_next(int p, int key) {
    if (!p) return INF;
    if (tr[p].key < key) return get_next(tr[p].r, key);
    return min(tr[p].key, get_next(tr[p].l, key));
}

int main() {
    build();
    scanf("%d", &n);
    
    LL res = 0;
    for (int i = 1; i <= n; ++i) {
        int x;
        scanf("%d", &x);
        if (i == 1) res += x;
        else res += min(x - get_prev(root, x), get_next(root, x) - x);
        
        insert(root, x);
    }
    
    printf("%lld\n", res);
    
    return 0;
}
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