洛谷 P816 忠诚 题解

每日一题 day28 打卡

Analysis

这道题用线段树维护区间最小值很简单，因为没有修改所以连lazy_tag都不用，但是这道题可以用树状数组维护区间最小值，非常骚气。

线段树代码：

 #include<iostream>
 #include<cstdio>
 #include<cstring>
 #include<algorithm>
 #include<cmath>
 #define int long long
 #define maxn 1000000+10
 using namespace std;
 inline int read()
 {
     int x=;
     bool f=;
     char c=getchar();
     for(; !isdigit(c); c=getchar()) if(c=='-') f=;
     for(; isdigit(c); c=getchar()) x=(x<<)+(x<<)+c-'';
     if(f) return x;
     return -x;
 }
 inline void write(int x)
 {
     if(x<){putchar('-');x=-x;}
     if(x>)write(x/);
     putchar(x%+'');
 }
 int m,n;
 int a[maxn];
 struct Segment_tree
 {
     struct Segment_tree_node
     {
         int l,r,val;
     }node[maxn*];
     int n;
     inline int size() {return n;}
     inline int left_s(int x) {return (x<<);}
     inline int right_s(int x) {return ((x<<)|);}
     inline void init(int l,int r)
     {
         n=r-l+;
         node[].l=;
         node[].r=n;
         build();
     }
     inline void push_up(int x)
     {
         node[x].val=min(node[left_s(x)].val,node[right_s(x)].val);
     }
     inline void build(int x)
     {
         if(node[x].l==node[x].r)
         {
             node[x].val=a[node[x].l];
             return;
         }
         int mid=(node[x].l+node[x].r)>>;
         node[left_s(x)].l=node[x].l;
         node[left_s(x)].r=mid;
         build(left_s(x));
         node[right_s(x)].l=mid+;
         node[right_s(x)].r=node[x].r;
         build(right_s(x));
         push_up(x);
     }
     inline int query(int x,int l,int r)
     {
         if(node[x].l==l&&node[x].r==r)
         {
             return node[x].val;
         }
         int mid=(node[x].l+node[x].r)>>;
         if(r<=mid) return query(left_s(x),l,r);
         if(l>mid) return query(right_s(x),l,r);
         return min(query(left_s(x),l,mid),query(right_s(x),mid+,r));
     }
 }t;
 signed main()
 {
     m=read();n=read();
     for(int i=;i<=m;i++) a[i]=read();
     t.init(,m);
     for(int i=;i<=n;i++)
     {
         int x=read(),y=read();
         int ans=t.query(,x,y);
         write(ans);
         printf(" ");
     }
     return ;
 }

树状数组代码：

 #include<iostream>
 #include<cstdio>
 #include<cstring>
 #include<algorithm>
 #include<cmath>
 #define int long long
 #define maxn 1000000+10
 #define INF 2147483647
 using namespace std;
 inline int read()
 {
     int x=;
     bool f=;
     char c=getchar();
     for(; !isdigit(c); c=getchar()) if(c=='-') f=;
     for(; isdigit(c); c=getchar()) x=(x<<)+(x<<)+c-'';
     if(f) return x;
     return -x;
 }
 inline void write(int x)
 {
     if(x<){putchar('-');x=-x;}
     if(x>)write(x/);
     putchar(x%+'');
 }
 int m,n;
 int a[maxn];
 int tree[maxn];
 inline int lowbit(int num)
 {
     return num&(-num);
 }
 inline void update(int s,int num)
 {
     int i=s;
     while(i<=m)
     {
         if(tree[i]>num)
             tree[i]=num;
         else return;
         i+=lowbit(i);
     }
 }
 inline int query(int l,int r)
 {
     int res=INF,i=r;
     while(i>=l)
     {
         if(i-lowbit(i)>l)
         {
             res=min(res,tree[i]);
             i-=lowbit(i);
         }
         else
         {
             res=min(res,a[i]);
             --i;
         }
     }
     return res;
  }
 signed main()
 {
     memset(tree,,sizeof(tree));
     m=read();n=read();
     for(int i=;i<=m;i++)
     {
         a[i]=read();
         update(i,a[i]);
     }
     for(int i=;i<=n;i++)
     {
         int x=read(),y=read();
         int ans=query(x,y);
         write(ans);
         printf(" ");
     }
     return ;
 }

请各位大佬斧正（反正我不认识斧正是什么意思）