【LOJ】#2432. 「POI2014」代理商 Couriers

题解

建出一个主席树，因为出现大于区间一半的数只能有一个，就看看左右区间的增加有没有大于一半，如果有就走向那个子树，如果没有那么返回0

代码

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <vector>
#include <set>
#include <cmath>
#include <bitset>
#include <queue>
#define enter putchar('\n')
#define space putchar(' ')
//#define ivorysi
#define pb push_back
#define mo 974711
#define pii pair<int,int>
#define mp make_pair
#define fi first
#define se second
#define MAXN 500005
#define eps 1e-12
using namespace std;
typedef long long int64;
typedef double db;
template<class T>
void read(T &res) {
    res = 0;char c = getchar();T f = 1;
    while(c < '0' || c > '9') {
	if(c == '-') f = -1;
	c = getchar();
    }
    while(c >= '0' && c <= '9') {
	res = res * 10 - '0' + c;
	c = getchar();
    }
    res = res * f;
}
template<class T>
void out(T x) {
    if(x < 0) {x = -x;putchar('-');}
    if(x >= 10) out(x / 10);
    putchar('0' + x % 10);
}
int N,M;
int a[MAXN];
struct node {
    int lc,rc;
    int siz;
}tr[MAXN * 80];
int Ncnt,rt[MAXN];
void Insert(int x,int &y,int L,int R,int pos) {
    y = ++Ncnt;
    tr[y] = tr[x];
    tr[y].siz++;
    if(L == R) return;
    int mid = (L + R) >> 1;
    if(pos <= mid) Insert(tr[x].lc,tr[y].lc,L,mid,pos);
    else Insert(tr[x].rc,tr[y].rc,mid + 1,R,pos);
}
int check(int L,int R) {
    int k = ((R - L + 1) / 2) + 1;
    int Lrt = rt[L - 1],Rrt = rt[R];
    int l = 1,r = N;
    while(l < r) {
	int mid = (l + r) >> 1;
	if(tr[tr[Rrt].lc].siz - tr[tr[Lrt].lc].siz >= k) {
	    Lrt = tr[Lrt].lc;Rrt = tr[Rrt].lc;
	    r = mid;
	}
	else if(tr[tr[Rrt].rc].siz - tr[tr[Lrt].rc].siz >= k) {
	    Lrt = tr[Lrt].rc;Rrt = tr[Rrt].rc;
	    l = mid + 1;
	}
	else {return 0;}
    }
    return l;
}
void Solve() {
    read(N);read(M);
    for(int i = 1 ; i <= N ; ++i) read(a[i]);
    for(int i = 1 ; i <= N ; ++i) Insert(rt[i - 1],rt[i],1,N,a[i]);
    int l,r;
    for(int i = 1 ; i <= M ; ++i) {
	read(l);read(r);
	out(check(l,r));enter;
    }
}
int main() {
#ifdef ivorysi
    freopen("f1.in","r",stdin);
#endif
    Solve();
}