【題解】洛谷 P1083 借教室

目錄

• 題目
• 思路
• $Code$

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題目

P1083 借教室

思路

線段樹。須要的操做爲區間修改，區間查詢。維護每一個區間的最小值就好。

$Code$

#include<iostream>
#include<cstring>
#include<string>
#include<cstdio>
#include<algorithm>
#define lson now<<1
#define rson now<<1|1
#define MAXN 1000001
#define rr register
#define min_(a,b) a>b?b:a
using namespace std;
int n,m;
struct Node{
    int l,r,minn;
    int lazy;
}tree[MAXN<<2];

inline void read(int &T) {
    int x=0;bool f=0;char c=getchar();
    while(c<'0'||c>'9'){if(c=='-')f=!f;c=getchar();}
    while(c>='0'&&c<='9'){x=x*10+c-'0';c=getchar();}
    T=f?-x:x;
}

inline void write(int x) {
    if(x<0) putchar('-'),write(-x);
    else {
        if(x/10) write(x/10);
        putchar(x%10+'0');
    }
}

void build(int l,int r,int now) {
    tree[now].l=l,tree[now].r=r;
    if(tree[now].l==tree[now].r) {
        read(tree[now].minn);
        return;
    }
    int mid=(tree[now].l+tree[now].r)>>1;
    build(l,mid,lson),build(mid+1,r,rson);
    tree[now].minn=min_(tree[lson].minn,tree[rson].minn);
}

inline void pushdown(int now) {
    if(tree[now].l==tree[now].r) return;
    tree[lson].lazy+=tree[now].lazy;
    tree[rson].lazy+=tree[now].lazy;
    tree[lson].minn-=tree[now].lazy;
    tree[rson].minn-=tree[now].lazy;
    tree[now].lazy=0;
}

int query(int x,int y,int now) {
    if(tree[now].l>=x&&tree[now].r<=y) {
        return tree[now].minn;
    }
    if(tree[now].lazy) pushdown(now);
    int mid=(tree[now].l+tree[now].r)>>1,minnn=0x7fffffff;
    if(x<=mid) minnn=min(minnn,query(x,y,lson));
    if(y>mid) minnn=min(minnn,query(x,y,rson));
    return minnn;
}

void update(int x,int y,int k,int now) {
    if(tree[now].l>=x&&tree[now].r<=y) {
        tree[now].minn-=k;
        tree[now].lazy+=k;
        return;
    }
    if(tree[now].lazy) pushdown(now);
    int mid=(tree[now].l+tree[now].r)>>1;
    if(x<=mid) update(x,y,k,lson);
    if(y>mid) update(x,y,k,rson);
    tree[now].minn=min_(tree[lson].minn,tree[rson].minn);
}

int main() {
    read(n),read(m);
    build(1,n,1);
    for(rr int i=1,x,y,k;i<=m;++i) {
        read(k),read(x),read(y);
        if(query(x,y,1)<k) {
            puts("-1");
            write(i);
            return 0;
        }else update(x,y,k,1);
    }
    puts("0");
    return 0;
}