线段[luogu3842][DP]

传送门

好水的DP , 直接转移就好了

---

#include<bits/stdc++.h>
#define N 20050
using namespace std;
int f[N][2],n,l[N],r[N],len[N];
int main(){
	scanf("%d",&n);
	for(int i=1;i<=n;i++) scanf("%d%d",&l[i],&r[i]) , len[i] = r[i] - l[i] + 1;
	f[1][0] = r[1] + len[1] - 1;
	f[1][1] = r[1] - 1;
	for(int i=2;i<=n;i++){
		int x1 = f[i-1][0] + abs(l[i-1] - r[i]) + len[i];
		int x2 = f[i-1][1] + abs(r[i-1] - r[i]) + len[i];
		f[i][0] = min(x1,x2);
		x1 = f[i-1][0] + abs(l[i-1] - l[i]) + len[i];
		x2 = f[i-1][1] + abs(r[i-1] - l[i]) + len[i];
		f[i][1] = min(x1,x2);
	}
	int x1 = f[n][0] + n - l[n];
	int x2 = f[n][1] + n - r[n];
	printf("%d",min(x1,x2)); return 0;
}