【POJ 3657】Haybale Guessing

Haybale Guessing

Time Limit: 1000MS		Memory Limit: 65536K
Total Submissions: 2093		Accepted: 567

Description

The cows, who always have an inferiority complex about their intelligence, have a new guessing game to sharpen their brains.

A designated 'Hay Cow' hides behind the barn and creates N (1 ≤ N ≤ 1,000,000) uniquely-sized stacks (conveniently numbered 1..N) of hay bales, each with 1..1,000,000,000 bales of hay.

The other cows then ask the Hay Cow a series of Q (1 ≤ Q ≤ 25,000) questions about the the stacks, all having the same form:

What is the smallest number of bales of any stack in the range of stack numbers Q_l..Q_h (1 ≤ Q_l ≤ N; Q_l ≤ Q_h ≤ N)?

The Hay Cow answers each of these queries with a single integer A whose truthfulness is not guaranteed.

Help the other cows determine if the answers given by the Hay Cow are self-consistent or if certain answers contradict others.

Input

* Line 1: Two space-separated integers: N and Q
* Lines 2..Q+1: Each line contains three space-separated integers that represent a single query and its reply: Q_l, Q_h, and A

Output

* Line 1: Print the single integer 0 if there are no inconsistencies among the replies (i.e., if there exists a valid realization of the hay stacks that agrees with all Q queries). Otherwise, print the index from 1..Q of the earliest query whose answer is inconsistent with the answers to the queries before it.

Sample Input

20 4
1 10 7
5 19 7
3 12 8
11 15 12

Sample Output

3

Source

USACO 2008 January Gold

 

此题有多种解法。我的是二分答案+线段树区间覆盖

假设当增加了第K句回答的时候会起冲突，求K的最小值，也就是说我们可以二分这个K。如果从1~第K句话会起冲突，那么我们可以看一下K前面会不会已经起了冲突了呢?如果第K句话并不会起冲突，那答案肯定就在K后面了。

然后我们如何检查是否已经起冲突呢？

很明显，大的A值会影响小的A值，为什么？假设A₁<A₂，那么很明显当A₁先覆盖了，A₂再覆盖的时候我们肯定会不好处理了，因为有很多种情况。

所以，我们可以用A₂先覆盖，然后和A₁区间的交集是不能覆盖的。（想想为什么）

我们可以从A值的大到小进行覆盖（即染色），查询一下，当前要覆盖的A值的区间是否已经全部被染色了，如果是，那么说明已经起了冲突。

时间复杂度有点大，是O(log₂Q * Qlog₂N)，好像比USACO的官方解法要慢，反正我也看不懂。

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;

const int MAXN = 1000005;
const int MAXQ = 25005;

struct Discret
{
    int a;
    int ID;

    bool operator < (const Discret &b) const
    {
        return a < b.a;
    }
}A[MAXQ];

int ql[MAXQ], qr[MAXQ];
int orig[MAXQ];
int leftv[2][MAXQ], rightv[2][MAXQ];
bool v[MAXN << 2];
int n, q;
int note;
int y1, y2;
bool flag;

void pushdown(int o)
{
    if (v[o])
    {
        int lc = o << 1, rc = lc + 1;
        v[lc] = v[rc] = v[o];
    }
}

void update(int o, int L, int R)
{
    if (y1 <= L && R <= y2) v[o] = true;
    else
    {
        pushdown(o);
        int mid = (L + R) >> 1;
        int lc = o << 1;
        int rc = lc + 1;
        if (mid >= y1) update(lc, L, mid);
        if (mid + 1 <= y2) update(rc, mid + 1, R);
        v[o] = v[lc] && v[rc];
    }
}

void query(int o, int L, int R)
{
    if (y1 <= L && R <= y2)
    {
        flag = flag && v[o];
        return;
    }
    pushdown(o);
    int mid = (L + R) >> 1;
    int lc = o << 1, rc = lc + 1;
    if (mid >= y1) query(lc, L, mid);
    if (mid + 1 <= y2) query(rc, mid + 1, R);
}

bool check(int qest)
{
    memset(v, false, sizeof(v));
    memset(leftv, 0x7f, sizeof(leftv));
    memset(rightv, 0, sizeof(rightv));
    for (int i = 1; i <= qest; ++i)
    {
        if (leftv[0][orig[i]] <= rightv[0][orig[i]])
        {
            leftv[0][orig[i]] = max(leftv[0][orig[i]], ql[i]);
            leftv[1][orig[i]] = min(leftv[1][orig[i]], ql[i]);
            rightv[0][orig[i]] = min(rightv[0][orig[i]], qr[i]);
            rightv[1][orig[i]] = max(rightv[1][orig[i]], qr[i]);
            if (leftv[0][orig[i]] > rightv[0][orig[i]]) return true;
        }
        else
        {
            leftv[0][orig[i]] = leftv[1][orig[i]] = ql[i];
            rightv[0][orig[i]] = rightv[1][orig[i]] = qr[i];
        }
    }
    for (int i = note; i >= 0; --i)
    {
        y1 = leftv[0][i];
        y2 = rightv[0][i];
        if (y1 <= y2)
        {
            flag = true;
            query(1, 1, n);
            if (flag) return true;
            y1 = leftv[1][i];
            y2 = rightv[1][i];
            update(1, 1, n);
        }
    }
    return false;
}

void binarySearch(int l, int r)
{
    if (l == r)
    {
        printf("%d
", l);
        return;
    }
    int mid = (l + r) >> 1;
    if (check(mid)) binarySearch(l, mid);
    else binarySearch(mid + 1, r);
}

int main()
{
    scanf("%d %d", &n, &q);
    for (int i = 1; i <= q; ++i) scanf("%d %d %d", &ql[i], &qr[i], &A[i].a), A[i].ID = i;
    sort(A + 1, A + q + 1);
    note = -1;
    int tmp = -1;
    for (int i = 1; i <= q; ++i)
        if (tmp < A[i].a) orig[A[i].ID] = ++note, tmp = A[i].a;
        else orig[A[i].ID] = note;
    if (check(q))
        binarySearch(1, q);
    else printf("0
");
    return 0;
}