同上一题，区间改左闭右开就双倍经验了。貌似可以跑最长路。
#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#define R(a,b,c) for(register int a = (b); a <= (c); ++ a)
#define nR(a,b,c) for(register int a = (b); a >= (c); -- a)
#define Max(a,b) ((a) > (b) ? (a) : (b))
#define Min(a,b) ((a) < (b) ? (a) : (b))
#define Fill(a,b) memset(a, b, sizeof(a))
#define Abs(a) ((a) < 0 ? -(a) : (a))
#define Swap(a,b) a^=b^=a^=b
#define ll long long#define ON_DEBUG#ifdef ON_DEBUG#define D_e_Line printf("\n\n----------\n\n")
#define D_e(x) cout << #x << " = " << x << endl
#define Pause() system("pause")
#define FileOpen() freopen("in.txt","r",stdin);#else#define D_e_Line ;
#define D_e(x) ;
#define Pause() ;
#define FileOpen() ;#endifstruct ios{template<typename ATP>ios& operator >> (ATP &x){x = 0; int f = 1; char c;for(c = getchar(); c < '0' || c > '9'; c = getchar()) if(c == '-') f = -1;while(c >= '0' && c <= '9') x = x * 10 + (c ^ '0'), c = getchar();x*= f;return *this;}
}io;
using namespace std;const int N = 10007;struct Field{int l, r, w;bool operator < (const Field &com) const{if(r != com.r) return r < com.r;return l < com.l;}
}a[N];int f[N];inline int Find(int x){int l = 1, r = x;int ans = -1;while(l <= r){int mid = (l + r) >> 1;if(a[mid].r < a[x].l){l = mid + 1;ans = mid;}else{r = mid - 1;}}return ans;
}
int main(){//FileOpen();int n;io >> n;R(i,1,n){io >> a[i].l >> a[i].r;--a[i].r;a[i].w = a[i].r - a[i].l + 1;}sort(a + 1, a + n + 1);f[1] = a[1].w;R(i,2,n){int j = Find(i);if(j != -1)f[i] = Max(f[i - 1], f[j] + a[i].w);elsef[i] = Max(f[i - 1], a[i].w);}printf("%d\n",f[n]);return 0;
}
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