poj3264

简单线段树 根节点存储最值；
不要存储差值 如果存储差值 在返回结果的时候有很多的麻烦，
所以在建树的过程中更新每个更节点的 最值，
最后直接比较区间的最值，

#include <iostream>
#include <cstdio>

using namespace std;
const int maxn = 50005;

#define LL(x) (x<<1)
#define RR(x) (x<<1|1)
#define MID(a, b) ((a+b)>>1)

struct node
{
    int lft, rht, hei, low, value;
    int mid()
    {
        return MID(lft, rht);
    }
};

int n, m, a[maxn];
int _max, _min;

struct Segtree
{
    node tree[maxn*4];
    void build(int lft, int rht, int inf)
    {
        tree[inf].lft = lft;
        tree[inf].rht = rht;
        if(lft == rht) tree[inf].hei = tree[inf].low = a[lft];
        else
        {
            int mid = tree[inf].mid();
            build(lft, mid, LL(inf));
            build(mid+1, rht, RR(inf));
            tree[inf].hei = max(tree[LL(inf)].hei, tree[RR(inf)].hei);
            tree[inf].low = min(tree[LL(inf)].low, tree[RR(inf)].low);
        }
    }
    void query(int st, int en, int inf)
    {
        if(st <= tree[inf].lft && tree[inf].rht <= en)
        {
            _max = max(_max, tree[inf].hei);
            _min = min(_min, tree[inf].low);
            return ;
        }
        int mid = tree[inf].mid();
        if(st <= mid) query(st, en, LL(inf));
        if(mid < en) query(st, en, RR(inf));
    }
} seg;

int main()
{
    while(scanf("%d %d", &n, &m) != EOF)
    {
        for(int i = 1; i <= n; i++) scanf("%d", a+i);
        seg.build(1, n, 1);
        for(int i = 1; i <= m; i++)
        {
            _max = -1;
            _min = 99999999;
            int u, v;
            scanf("%d%d", &u, &v);
            seg.query(u, v, 1);
            printf("%d\n", _max-_min);
        }
    }
}