关于二分的学习

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关于二分的解释：
练习题目：
愤怒的牛

题解

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

int a[100005], n, m;

bool check(int x){
	int cow = 1;
	int sum = a[1] + x;
	for(int i = 2; i <= n; i++)
	{
		if(a[i] < sum) continue;
		cow++;
		sum = a[i] + x;
	}
	if(cow >= m) return true;
	else return false;
}
int main()
{
	scanf("%d %d",&n, &m);
	for(int i = 1; i <= n; i++)
		scanf("%d",&a[i]);
	sort(a+1, a+n+1);
	int l = 0, r = a[n] - a[1];
	int mid, ans;
	while(l <= r)
	{
		mid = (l+r) / 2;
		if(check(mid) == true)
		{
			l = mid + 1;
			ans = mid;
		}
		else r = mid - 1;
	}
	printf("%d\n",ans);
	return 0;
}

Best Cow Fences
题解

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

long long a[100005], s[100005];
long long n, L;
long long ans;

bool check(long long x){
	for(int i = 1; i <= n; i++)
		s[i] = s[i-1] + a[i] - x; 
	long long minn = 99999999;
	for(int i = L; i <= n; i++)
	{
		minn = min(minn, s[i-L]);
		if(s[i] - minn >= 0) return true; 
	}
	return false;
}
int main()
{
	scanf("%d %d",&n, &L);
	long long l, r;
	for(int i = 1; i <= n; i++)
	{
		scanf("%d",&a[i]);
		a[i] *= 1000;
		l = min(l, a[i]);
		r = max(r, a[i]);
	}
	while(l <= r)
	{
		int mid = (l+r) / 2;
		if(check(mid) == true)
		{
			l = mid+1;
			ans = mid;
		}
		else r = mid - 1; 
	}	
	printf("%d\n",ans);	
 } 

数列分段二
题解

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

int n, m;
int a[1000005];

bool check(int x)  
{
	int k = 1, sum = 0; // k是组数  
	for(int i = 1; i <= n; i++) 
	{
		if(sum + a[i] > x)// 加上a[i]若超过中间数 就将这个数分入下一组 
		{
			sum = a[i]; 
			k++; // 组数+1 
		}
		else sum += a[i];
	}
	if(k <= m) return true; // 不能超过m段 
	return false; 
}
int main()
{
	scanf("%d %d",&n, &m);
	int l = 0, r = 0, ans = 0;
	for(int i = 1; i <= n; i++)
	{
		scanf("%d",&a[i]);
		r += a[i]; // 最大值(右边界)等于所有数的和 
		l = max(l, a[i]); // 最小值(左边界)等于单个的最大值 
	}
	while(l <= r)
	{
		int mid = (l+r) / 2;
		if(check(mid) == true) // 要求找最小值 
		{
			ans = mid;
			r = mid-1; // 往左边找（小一点的） 
		}
		else l = mid+1;// 往右边找（大一点的） 
	}
	printf("%d\n",ans);
	return 0;
}

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