19728 拼十字

19728 拼十字

⭐️难度：中等
🌟考点：树状数组、省赛、2024
📖

📚

import java.io.*;
import java.util.*;

public class Main {
    static class FenwickTree {
        int n;
        int[] tree;

        public FenwickTree(int n) {
            this.n = n;
            tree = new int[n + 1];
        }

        int lowbit(int i) {
            return i & -i;
        }

        void add(int i, int val) {
            for (; i <= n; i += lowbit(i)) {
                tree[i] += val;
            }
        }

        int preSum(int i) {
            int ret = 0;
            for (; i > 0; i -= lowbit(i)) {
                ret += tree[i];
            }
            return ret;
        }

        int rangeSum(int l, int r) {
            return preSum(r) - preSum(l - 1);
        }
    }

    static int maxn = 100010;
    static int ans = 0;
    static int mod = (int) 1e9 + 7;

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        List<int[]> arr = new ArrayList<>();

        // 读入所有的矩形
        for (int i = 0; i < n; i++) {
            int l = sc.nextInt(); // 长
            int w = sc.nextInt(); // 宽
            int c = sc.nextInt(); // 颜色
            arr.add(new int[]{l, w, c});
        }

        // 对矩形进行排序，l升序，然后w升序
        arr.sort((o1, o2) -> {
            if (o1[0] != o2[0]) return Integer.compare(o1[0], o2[0]);
            else return Integer.compare(o1[1], o2[1]);
        });

        // 建立三种颜色对应的树状数组
        FenwickTree[] tree = new FenwickTree[3];
        for (int i = 0; i < 3; i++) tree[i] = new FenwickTree(maxn);

        // 然后枚举排序好的arr
        for (int[] a : arr) {
            int l = a[0];
            int w = a[1];
            int c = a[2];
            for (int i = 0; i < 3; i++) {
                if (c == i) continue; // 相同颜色被排除掉
                ans = (ans + tree[i].rangeSum(w + 1, maxn)) % mod; // 累加答案
            }
            tree[c].add(w, 1); // 更新树状数组
        }
        System.out.println(ans);
    }
}