NOIP2012 借教室 （线段树）

Description

Solution

考虑用线段树维护，每借一段时间的教师便在线段树中减去对应的值，不理解为什么网上这么多二分的。。

Code

//Author: Hany01//Date: Nov 5th. 2017#include<bits/stdc++.h>#define For(i , j , k) for (int i = (j) , i##_end_ = (k) ; i <= i##_end_ ; ++ i)#define Fordown(i , j , k) for (int i = (j) , i##_end_ = (k) ; i >= i##_end_ ; -- i)#define Set(a , b) memset(a , b , sizeof(a))#define lc (t << 1)#define rc (lc | 1)#define mid ((l + r) >> 1)#define pb push_back#define INF (0x3f3f3f3f)#define Mod (1000000007)using namespace std;typedef long long LL;template <typename T> inline bool chkmax(T &a , T b) { return a < b ? (a = b , 1) : 0; }template <typename T> inline bool chkmin(T &a , T b) { return b < a ? (a = b , 1) : 0; }int _ , __;char c_;inline int read(){    for (_ = 0 , __ = 1 , c_ = getchar() ; !isdigit(c_) ; c_ = getchar()) if (c_ == '-') __ = -1;    for ( ; isdigit(c_) ; c_ = getchar()) _ = (_ << 1) + (_ << 3) + (c_ ^ 48);    return _ * __;}inline void File(){#ifdef hany01    freopen("classroom.in" , "r" , stdin);    freopen("classroom.out" , "w" , stdout);#endif}const int maxn = 1000010;int tr[maxn << 2], addv[maxn << 2], n, m, dt, x, y;inline void maintain(int t) { tr[t] = min(tr[lc], tr[rc]); }inline void pushdown(int t){    if (!addv[t]) return ;    tr[lc] += addv[t]; tr[rc] += addv[t]; addv[lc] += addv[t]; addv[rc] += addv[t]; addv[t] = 0;}void build(int t, int l, int r){    if (l == r) { tr[t] = read(); return; }    build(lc, l, mid); build(rc, mid + 1, r);    maintain(t);}void update(int t, int l, int r){    if (x <= l && r <= y) { tr[t] += dt; addv[t] += dt; return; }    pushdown(t);    if (x <= mid) update(lc, l, mid);    if (y > mid)  update(rc, mid + 1, r);    maintain(t);}int main(){    File();    n = read(); m = read();    build(1, 1, n);    For(Case, 1, m)    {        dt = -read(); x = read(); y = read();        update(1, 1, n);        if (tr[1] < 0) { printf("-1\n%d\n", Case); return 0; }    }    puts("0");    return 0;}//静夜四无邻，荒居旧业贫。//雨中黄叶树，灯下白头人。//以我独沉久，愧君相见频。//平生自有分，况是霍家亲。//--司空曙《喜见外弟卢纶见宿》