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
     
      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
      
       #define pli pair
       
        #define pii pair
        
         #define piii pair
         
          #define pdi pair
          
           #define pdd pair
           
            #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);//headconst 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;}