差分约束[SCOI2008]天平

这个差分约束真的想不到，说白了就是统计C和D

https://www.luogu.com.cn/problem/P2474

哎不说了，建议看看原来的题解

 

 

#include<iostream>
#include<cstring>
#include<algorithm>
#include<cstdio>
using namespace std;
int dm[55][55];
int dx[55][55];
int n, a, b;
char cn[55];
int main() {
	scanf("%d%d%d", &n, &a, &b);
	for (int i = 1; i <= n; i++) {
		scanf("%s", cn + 1);
		int len = strlen(cn + 1);

		for (int j = 1; j<=len; j++) {

			if (i == j || cn[j] == '=') {
				dx[i][j] = 0;
				dm[i][j] = 0;
			}
			else if (cn[j] == '+') {
				dx[i][j] = 2;
				dm[i][j] = 1;
			}
			else if (cn[j] == '-') {
				dx[i][j] = -1;
				dm[i][j] = -2;
			}
			else {
				dx[i][j] = 2;
				dm[i][j] = -2;
			}
		}
	}
	for (int k = 1; k <= n; k++) {
		for (int i = 1; i <= n; i++) {
			for (int j = 1; j <= n; j++) {
				
				dx[i][j] = min(dx[i][k] + dx[k][j], dx[i][j]);
				dm[i][j] = max(dm[i][k] + dm[k][j], dm[i][j]);
			}
		}
	}
	int cnt1 = 0, cnt2=0, cnt3 = 0;

	for (int i = 1; i <= n; i++) {
		if (i == a || i == b) continue;

		for (int j = 1; j< i ; j++) {
			if (j == a || j == b || i == j)  continue;

			if (dm[a][i] > dx[j][b] || dm[b][i] > dx[j][a]) {
				cnt1++;
			}
			if ((dm[a][i] == dx[a][i] && dm[b][j] == dx[b][j] && dm[a][i] == dx[j][b]) || (dm[b][i] == dx[b][i] && dm[a][j] == dx[a][j] && dm[b][i] == dx[j][a])) {
				cnt2++;
			}
			
			if (dx[a][i] < dm[j][b] || dx[b][i] < dm[j][a]) {
				cnt3++;
			}
		}
	}
	cout << cnt1 << " " << cnt2 << " " << cnt3 << endl;
	return 0;
}