题目大意
给出一个序列,问一段区间内有没有出现过一半以上的数字。
思路
用主席树取区间出来,在权值线段树上找。
CODE
#define _CRT_SECURE_NO_WARNINGS
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#define MAX 500010
#define MAXR 10000010
using namespace std;
struct SegTree{
SegTree *son[2];
int cnt;
}mempool[MAXR], *C = mempool, *root[MAX];
SegTree *NewSegTree(SegTree *_, SegTree *__, int ___)
{
C->son[0] = _;
C->son[1] = __;
C->cnt = ___;
return C++;
}
SegTree *Insert(SegTree *consult, int l, int r, int x)
{
if(l == r)
return NewSegTree(consult->son[0], consult->son[1], consult->cnt + 1);
int mid = (l + r) >> 1;
if(x <= mid)
return NewSegTree(Insert(consult->son[0], l, mid, x), consult->son[1], consult->cnt + 1);
else
return NewSegTree(consult->son[0], Insert(consult->son[1], mid + 1, r, x), consult->cnt + 1);
}
int Ask(SegTree *left, SegTree *right, int l, int r, int c)
{
if(l == r) return l;
int mid = (l + r) >> 1;
if(right->son[0]->cnt - left->son[0]->cnt > c)
return Ask(left->son[0], right->son[0], l, mid, c);
else if(right->son[1]->cnt - left->son[1]->cnt > c)
return Ask(left->son[1], right->son[1], mid + 1, r, c);
return 0;
}
int cnt, asks;
int main()
{
root[0] = NewSegTree(C, C, 0);
cin >> cnt >> asks;
for(int x, i = 1; i <= cnt; ++i) {
scanf("%d", &x);
root[i] = Insert(root[i - 1], 1, cnt, x);
}
for(int x, y, i = 1; i <= asks; ++i) {
scanf("%d%d", &x, &y);
printf("%d\n", Ask(root[x - 1], root[y], 1, cnt, (y - x + 1) / 2));
}
return 0;
}
时间: 2024-10-02 23:12:45