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线段树+离线 hdu5654 xiaoxin and his watermelon candy

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题意:一个三元组假设满足j=i+1,k=j+1,ai<=aj<=ak,那么就好的。如今告诉你序列。然后Q次询问。每次询问一个区间[l,r],问区间里有多少个三元组满足要求

思路:刚開始看错题目了,原来三元组是连续3个,这作为bc最后一题也太水了把。

先一遍预处理。把连续3个满足条件的找出来,放到还有一个数组里排序去重,用这个数组来给三元组哈希。再扫一遍给三元组在之前那个排序好的数组里二分一下得到下标,大概就是哈希一下,用一个数字来表示。

之后的查询。事实上就是。在区间内。不同的数字有多少个。

这是一个很经典的线段树+离线的题目,仅仅要按右区间排序,然后xjb搞即可了,就不多说了。

#include <map>
#include <set>
#include <cmath>
#include <ctime>
#include <stack>
#include <queue>
#include <cstdio>
#include <cctype>
#include <string>
#include <vector>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <algorithm>
#include <functional>
#define fuck(x) cout<<"["<<x<<"]"
#define FIN freopen("input.txt","r",stdin)
#define FOUT freopen("output.txt","w+",stdout)
using namespace std;
typedef long long LL;
typedef pair<int, int> PII;

const int MX = 2e5 + 5;

struct Data {
    int a, b, c;
    bool operator<(const Data &P) const {
        if(a == P.a) {
            if(b == P.b) return c < P.c;
            return b < P.b;
        }
        return a < P.a;
    }
    bool operator==(Data &P) const {
        return a == P.a && b == P.b && c == P.c;
    }
} D[MX], dt;
struct Seg {
    int l, r, id;
    bool operator<(const Seg &P) const {
        return r < P.r;
    }
} S[MX];
int n, Q, ans[MX];
int sum[MX << 2], col[MX << 2];
int A[MX], pre[MX], pos[MX], sz;

#define lson l, m, rt << 1
#define rson m + 1, r, rt << 1 | 1
void push_up(int rt) {
    sum[rt] = sum[rt << 1] + sum[rt << 1 | 1];
}
void push_down(int rt, int len) {
    if(col[rt]) {
        int sr = len >> 1, sl = len - sr;
        col[rt << 1] += col[rt]; col[rt << 1 | 1] += col[rt];
        sum[rt << 1] += col[rt] * sl; sum[rt << 1 | 1] += col[rt] * sr;
        col[rt] = 0;
    }
}
void build(int l, int r, int rt) {
    sum[rt] = col[rt] = 0;
    if(l == r) return;
    int m = (l + r) >> 1;
    build(lson); build(rson);
}
int query(int p, int l, int r, int rt) {
    if(l == r) return sum[rt];
    int m = (l + r) >> 1;
    push_down(rt, r - l + 1);
    if(p <= m) return query(p, lson);
    else return query(p, rson);
}
void update(int L, int R, int l, int r, int rt) {
    if(L <= l && r <= R) {
        sum[rt] += r - l + 1;
        col[rt] += 1;
        return;
    }
    int m = (l + r) >> 1;
    push_down(rt, r - l + 1);
    if(L <= m) update(L, R, lson);
    if(R > m) update(L, R, rson);
    push_up(rt);
}

int main() {
    int T; //FIN;
    scanf("%d", &T);
    while(T--) {
        sz = 0;
        scanf("%d", &n);
        build(1, n, 1);

        for(int i = 1; i <= n; i++) scanf("%d", &A[i]);
        for(int i = 3; i <= n; i++) {
            if(A[i - 2] <= A[i - 1] && A[i - 1] <= A[i]) {
                sz++;
                D[sz].a = A[i - 2]; D[sz].b = A[i - 1]; D[sz].c = A[i];
            }
        }
        sort(D + 1, D + 1 + sz);
        sz = unique(D + 1, D + 1 + sz) - D - 1;
        for(int i = 1; i <= sz; i++) pos[i] = 0;
        for(int i = 1; i <= n; i++) {
            if(i >= 3 && A[i - 2] <= A[i - 1] && A[i - 1] <= A[i]) {
                dt.a = A[i - 2]; dt.b = A[i - 1]; dt.c = A[i];
                int id = lower_bound(D + 1, D + 1 + sz, dt) - D;
                pre[i] = pos[id];
                pos[id] = i;
            } else pre[i] = -1;
        }

        scanf("%d", &Q);
        for(int i = 1; i <= Q; i++) {
            S[i].id = i;
            scanf("%d%d", &S[i].l, &S[i].r);
        }
        sort(S + 1, S + 1 + Q);

        int cur = 1;
        for(int r = 1; r <= n; r++) {
            if(pre[r] != -1) update(pre[r] + 1, r, 1, n, 1);
            while(cur <= Q && S[cur].r == r) {
                if(S[cur].l + 2 <= S[cur].r) ans[S[cur].id] = query(S[cur].l + 2, 1, n, 1);
                else ans[S[cur].id] = 0;
                cur++;
            }
        }

        for(int i = 1; i <= Q; i++) printf("%d\n", ans[i]);
    }
    return 0;
}


线段树+离线 hdu5654 xiaoxin and his watermelon candy