poj3264 线段树求最大值，最小值

最新推荐文章于 2019-11-22 18:40:06 发布

原创最新推荐文章于 2019-11-22 18:40:06 发布 · 312 阅读

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本文介绍了一种使用线段树实现区间最大值和最小值查询的高效算法。该算法适用于处理大规模数据集上的动态范围查询问题，通过预处理将查询时间复杂度降低到对数级别。

#include <iostream>
#include<stdio.h>
using namespace std;
const int maxn=50000+5;
int n,q;
int height[maxn];
struct segtree
{
int left,right;
int maxx,minn;
};
segtree tree[maxn*4];

void build(int low,int high,int index)
{
    tree[index].left=low;
    tree[index].right=high;
    if(low==high)
    {
        tree[index].maxx=height[low];
        tree[index].minn=height[low];
        return;
    }
    else
    {
        int mid=(low+high)/2;
        build(low,mid,index*2);
        build(mid+1,high,index*2+1);
        tree[index].maxx=max(tree[index*2].maxx,tree[index*2+1].maxx);
        tree[index].minn=min(tree[index*2].minn,tree[index*2+1].minn);
    }
}

int qmax(int low,int high,int index)
{
if(tree[index].left==low&&tree[index].right==high)
{
      return tree[index].maxx;
}
else
{
      int mid=(tree[index].left+tree[index].right)/2;
      if(high<=mid)
      {
          return qmax(low,high,index*2);
      }
      else if(low>mid)
      {
          return qmax(low,high,index*2+1);
      }
      else
      {
          return max(qmax(low,mid,index*2),qmax(mid+1,high,index*2+1));
      }
}
}

int qmin(int low,int high,int index)
{
    if(tree[index].left==low&&tree[index].right==high)
{
      return tree[index].minn;
}
else
{
      int mid=(tree[index].left+tree[index].right)/2;
      if(high<=mid)
      {
          return qmin(low,high,index*2);
      }
      else if(low>mid)
      {
          return qmin(low,high,index*2+1);
      }
      else
      {
          return min(qmin(low,mid,index*2),qmin(mid+1,high,index*2+1));
      }
}
}

int main()
{
   scanf("%d%d",&n,&q);
   for(int i=1;i<=n;i++)
    scanf("%d",&height[i]);
   build(1,n,1);
   while(q--)
   {
       int a,b;
       scanf("%d%d",&a,&b);
       printf("%d\n",qmax(a,b,1)-qmin(a,b,1));
   }
    return 0;
}