Codeforces 101B Buses 排序+树状数组

题目链接：点击打开链接

当转移[l,r] 区间时， 若[0, r-1] 这里的区间都已经转移完毕时是最优的，所以按右端点升序，同理右端点相同时左端点升序，然后树状数组维护一下前缀和。

#include <vector>
#include <iostream>
#include <algorithm>
#include <string.h>
#include <stdio.h>
using namespace std;
#define N 100005
#define mod 1000000007
#define ll long long
int n, m;
ll c[N<<2];
inline int lowbit(int x){return x&(-x);}
void updata(ll val, int pos){
	while(pos <= n){
		c[pos] = (c[pos] + val)%mod;
		pos += lowbit(pos);
	}
}
ll sum(int pos){
	ll ans = 0;
	while(pos){
		ans = (ans + c[pos])%mod;
		pos -= lowbit(pos);
	}
	return ans;
}
struct node{
	int l, r;
}a[N];
bool cmp1(node x, node y){if(x.r==y.r)return x.l<y.l; return x.r < y.r;}
vector<int>G;
void debug(){
    for(int i = 0; i < m; i++)printf("  %d %d\n", a[i].l, a[i].r);
    printf("***");
    for(int i = 0; i < G.size(); i++) printf("%d ", G[i]); puts("");
    printf("** n = %d\n", n);
}
void input(){
    n++;
	G.clear(); G.push_back(1); G.push_back(n);
	for(int i = 0; i < m; i++)scanf("%d %d", &a[i].l, &a[i].r),a[i].l++, a[i].r++, G.push_back(a[i].l), G.push_back(a[i].r);
	sort(G.begin(), G.end());
	G.erase(unique(G.begin(), G.end()), G.end());
//	debug();
	for(int i = 0; i < m; i++)
	{
		a[i].l = lower_bound(G.begin(), G.end(), a[i].l) - G.begin()+1;
		a[i].r = lower_bound(G.begin(), G.end(), a[i].r) - G.begin()+1;
	}
	n = lower_bound(G.begin(), G.end(), n) - G.begin()+1;
	sort(a, a+m, cmp1);
}
int main(){
	int i, j;
	while(~scanf("%d %d",&n,&m)){
   //     bool ok = n==42;
		input();
		if(m==0 || G.size()==1){puts("0");continue;}
	//	debug();
		memset(c, 0, sizeof c);
		updata(1, 1);
		for(i = 0; i < m; i++){
			ll ans = sum(a[i].r-1) - sum(a[i].l-1); if(ans < 0)	ans = (ans%mod + mod)%mod;
		//	printf("    %d %d %d\n", a[i].l, a[i].r, ans);
			updata(ans, a[i].r);
		//	printf("    %d %d %d\n", a[i].l, a[i].r, sum(a[i].r) - sum(a[i].l-1));
		}

		ll ans = sum(n) - sum(n-1);
	//	printf("%d\n", ans);
        if(ans < 0)	ans = (ans%mod + mod)%mod;
		cout<<ans<<endl;
	}
	return 0;
}
/*
4 4
0 2
1 3
1 4
2 4

4 2
0 2
1 3

ans:
4
4
0

*/