POJ 1991 Turning in Homework（区间DP）

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <functional>

using namespace std;

#define rep(i, a, b)	for (int i(a); i <= (b); ++i)
#define dec(i, a, b)	for (int i(a); i >= (b); --i)
#define MP		make_pair
#define fi		first
#define se		second


typedef long long LL;

const int N = 1010;
int n, m, ed, ans;
pair <int, int> a[N];
int f[N][N][2];


int main(){

	scanf("%d%d%d", &n, &m, &ed);
	rep(i, 1, n) scanf("%d%d", &a[i].fi, &a[i].se);
	sort(a + 1, a + n + 1);

	f[1][n][0] = max(a[1].fi, a[1].se);
	f[1][n][1] = max(a[n].fi, a[n].se);

	dec(d, n - 1, 1){
		rep(i, 1, n - d + 1){
			int j = i + d - 1;
			f[i][j][0] = 1 << 30;
			if (j < n) f[i][j][0] = min(f[i][j][0], max(f[i][j + 1][1] + a[j + 1].fi - a[i].fi, a[i].se));
			if (i > 1) f[i][j][0] = min(f[i][j][0], max(f[i - 1][j][0] + a[i].fi - a[i - 1].fi, a[i].se));
		       	
			f[i][j][1] = 1 << 30;
			if (i > 1) f[i][j][1] = min(f[i][j][1], max(f[i - 1][j][0] + a[j].fi - a[i - 1].fi, a[j].se));
			if (j < n) f[i][j][1] = min(f[i][j][1], max(f[i][j + 1][1] + a[j + 1].fi - a[j].fi, a[j].se));
		}
	}

	ans = 1 << 30;
	rep(i, 1, n) ans = min(ans, min(f[i][i][0], f[i][i][1]) + abs(a[i].fi - ed));
	printf("%d\n", ans);
	return 0;
}