sicily--1145. 校门外的树

一开始没看到起点是0就 WA 了2次，其余没什么了

#include<iostream>
#include<cstring>
using namespace std;

int main()
{
	int tree[10001];//奢侈点，哈哈
	memset(tree, 0, sizeof(tree));//1表示种有树
	int length, num;
	cin >> length >> num;
	for(int i = 0; i <= length;i++)
	{
		tree[i] = 1;
	}
	for(int j = 0; j < num; j++)
	{
		int start, end;
		cin >> start >> end;
		for(int k = start; k <= end; k++)
		{
			tree[k] = 0;
		}
	}
	int sum = 0;//表示最终剩余的树
	for(int j = 0; j <= length; j++)
		sum = sum + tree[j];

	cout << sum << endl;
	return 0;
}