HDU 6521 Party

6521

思路：

线段树玄学剪枝， 俗称吉司机线段树。

代码：

#pragma GCC optimize(2)
#pragma GCC optimize(3)
#pragma GCC optimize(4)
#include<bits/stdc++.h>
using namespace std;
#define y1 y11
#define fi first
#define se second
#define pi acos(-1.0)
#define LL long long
#define ls rt<<1, l, m
#define rs rt<<1|1, m+1, r
//#define mp make_pair
#define pb push_back
#define ULL unsigned LL
#define pll pair<LL, LL>
#define pli pair<LL, int>
#define pii pair<int, int>
#define piii pair<pii, int>
#define pdi pair<double, int>
#define pdd pair<double, double>
#define mem(a, b) memset(a, b, sizeof(a))
#define debug(x) cerr << #x << " = " << x << "\n";
#define fio ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
//head

const int N = 5e5 + 5;
LL sum[N<<2];
int mn[N<<2];
int n, m, l, r;
void push_up(int rt) {
    mn[rt] = min(mn[rt<<1], mn[rt<<1|1]);
    sum[rt] = sum[rt<<1] + sum[rt<<1|1];
}
void build(int rt, int l, int r) {
    if(l == r) {
        sum[rt] = 0;
        mn[rt] = l;
        return ;
    }
    int m = l+r >> 1;
    build(ls);
    build(rs);
    push_up(rt);
}
LL query(int L, int R, int rt, int l, int r) {
    LL ans = 0;
    if(mn[rt] >= R) return 0;
    if(l == r) {
        ans = R-mn[rt];
        mn[rt] = R;
        return ans;
    }
    int m = l+r >> 1;
    if(L <= m) ans += query(L, R, ls);
    if(R > m) ans += query(L, R, rs);
    push_up(rt);
    return ans;
}
int main() {
    while(~scanf("%d %d", &n, &m)) {
        build(1, 1, n);
        for (int i = 1; i <= m; ++i) {
            scanf("%d %d", &l, &r);
            printf("%lld\n", query(l, r, 1, 1, n));
        }
    }
    return 0;
}