线段树求最值

问题描述：

For the daily milking, Farmer John's N cows (1 ≤ N ≤ 50,000) always line up in the same order. One day Farmer John decides to organize a game of Ultimate Frisbee with some of the cows. To keep things simple, he will take a contiguous range of cows from the milking lineup to play the game. However, for all the cows to have fun they should not differ too much in height.

Farmer John has made a list of Q (1 ≤ Q ≤ 200,000) potential groups of cows and their heights (1 ≤ height ≤ 1,000,000). For each group, he wants your help to determine the difference in height between the shortest and the tallest cow in the group.

Input

Line 1: Two space-separated integers, N and Q.
Lines 2..N+1: Line i+1 contains a single integer that is the height of cow i
Lines N+2..N+Q+1: Two integers A and B (1 ≤ A ≤ B ≤ N), representing the range of cows from A to B inclusive.

Output

Lines 1..Q: Each line contains a single integer that is a response to a reply and indicates the difference in height between the tallest and shortest cow in the range.

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样例输入：

6 3
1
7
3
4
2
5
1 5
4 6
2 2

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样例输出：

6
3
0

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原因分析：

用线段树求区间最值。

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解决方案：

#include "stdio.h"
#include "algorithm"
using namespace std;
const int N=5*1e4+110;
int d[N],x[N],a[N];
int n,m;
int lowbit(int x)
{
	return x&(-x);
}
void init()
{
	int i,j;
	for(i=1;i<=n;i++)
	{
		scanf("%d",&a[i]);
		d[i]=x[i]=a[i];
		for(j=1;j<lowbit(i);j<<=1)
		{
			d[i]=max(d[i],d[i-j]);
			x[i]=min(x[i],x[i-j]);
		}
	}
}
int find(int l,int r)
{
	int maxx,minn;
	minn=maxx=a[r];
	while(l!=r)
	{
		for(r-=1;r-l>=lowbit(r);r-=lowbit(r))
		{
			maxx=max(maxx,d[r]);
			minn=min(minn,x[r]);
		}
		maxx=max(maxx,a[r]);
		minn=min(minn,a[r]);
	}
	return maxx-minn;
}
int main ()
{
	int i,x,y;
	scanf("%d%d",&n,&m);
	init();
	for(i=1;i<=m;i++)
	{
		scanf("%d%d",&x,&y);
		printf("%d\n",find(x,y));
	}
	return 0;
}