1270. 数列区间最大值（climits用法+线段树模板题）

Posted 2021-03-09 doubest

题目链接：

https://www.acwing.com/problem/content/1272/

 

题解：

线段树模板题，单点求和、区间查询都可

 

AC代码：

#include <cstdio>
#include <iostream>
#include <algorithm>
#include <cstring>
#include <climits>

using namespace std;

const int N = 1e5+10;

int a[N];

struct Node{
    int l,r;
    int maxv;
}tr[N*4];

int n,m;
void pushup(int i){
    tr[i].maxv = max(tr[2*i].maxv , tr[2*i+1].maxv);
}


void build(int g,int l,int r){
    if(l >= r) tr[g] = {l,r,a[l]};
    else{
        int mid = (l+r) / 2;
        tr[g] = {l,r};
        build(g*2,l,mid);
        build(g*2+1,mid+1,r);
        pushup(g);
    }
    
}


int query(int g,int l,int r){
    int maxv = INT_MIN;
    int mid = (tr[g].l + tr[g].r) / 2;
    if(l <= tr[g].l && tr[g].r <= r) return tr[g].maxv;
    else{
        if(l <= mid) maxv = max(maxv,query(g*2,l,r));
        if(mid < r) maxv = max(maxv,query(g*2+1,l,r));
    }
    
    return maxv;
}


int main(){
    scanf("%d%d",&n,&m);
    for(int i=1;i<=n;i++) scanf("%d",&a[i]);
    build(1,1,n);

    int l,r;
    while(m--){
        scanf("%d%d",&l,&r);
        // printf("%d %d
",l,r);
        printf("%d
",query(1,l,r));
        // exit(0);
    }
    
    return 0;
}