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hdu5124——lines

2024-08-05 06:46:57   218人阅读

lines

Time Limit: 5000/2500 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 330    Accepted Submission(s): 155


Problem Description
John has several lines. The lines are covered on the X axis. Let A is a point which is covered by the most lines. John wants to know how many lines cover A.
 

Input
The first line contains a single integer T(1≤T≤100)(the data for N>100 less than 11 cases),indicating the number of test cases.
Each test case begins with an integer N(1≤N≤105),indicating the number of lines.
Next N lines contains two integers Xi and Yi(1≤Xi≤Yi≤109),describing a line.
 

Output
For each case, output an integer means how many lines cover A.
 

Sample Input
2
5
1 2 
2 2
2 4
3 4
5 1000
5
1 1
2 2
3 3
4 4
5 5
 

Sample Output
3
1
 

Source
BestCoder Round #20
 

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Statistic | Submit | Discuss | Note


比赛时一开始用线段树WA了，然后树状数组过的，赛后听某牛说可以O(n)，然后仔细想了下，比如现在要在[l，r]上覆盖一次，那么我们可以在s[l]上+1，s[r + 1] 上 - 1，记录覆盖次数，然后for一遍，当前的s[i] 加上 s[i - 1]就是i这个点被覆盖的次数，因为有s[r + 1] --，所以此方案是合理的，数据太大可以离散化一下


#include <map>
#include <set>
#include <list>
#include <queue>
#include <stack>
#include <vector>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <algorithm>

using namespace std;

const int N = 100010;

int xis[N << 1];
int po[N << 1];

struct node
{
	int l, r;
}lines[N];

int main()
{
	int t, n, cnt, res, ans;
	scanf("%d", &t);
	while (t--)
	{
		scanf("%d", &n);
		map <int, int> newx;
		memset (xis, 0, sizeof(xis));
		newx.clear();
		cnt = 0;
		res = 0;
		for (int i = 0; i < n; ++i)
	 	{
		 	scanf("%d%d", &lines[i].l, &lines[i].r);
		 	po[cnt++] = lines[i].l;
		 	po[cnt++] = lines[i].r;
	 	} 
	 	sort (po, po + cnt);
	 	for (int i = 0; i < cnt; ++i)
	 	{
	 		if (i == 0)
	 		{
	 			newx[po[i]] = ++res;
	 		}
	 		else if(po[i] == po[i - 1])
	 		{
	 			newx[po[i]] = newx[po[i - 1]];
	 		}
	 		else
	 		{
	 			newx[po[i]] = ++res;
	 		}
	 	}
	 	for (int i = 0; i < n; ++i)
	 	{
	 		int l = newx[lines[i].l];
	 		int r = newx[lines[i].r];
	 		xis[l]++;
	 		xis[r + 1]--;
	 	}
	 	ans = 0;
	 	for (int i = 1; i <= res; ++i)
	 	{
	 		xis[i] += xis[i - 1];
	 		if (ans < xis[i])
	 		{
	 			ans = xis[i];
	 		}
	 	}
	 	printf("%d\n", ans);
	}
	return 0;
}


hdu5124——lines


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