差分约束系统-优快云博客

本文链接：https://blog.youkuaiyun.com/fumingxiaoshen/article/details/125192943

差分约束系统

#include<iostream>
#include<cstring>
#include<queue>
using namespace std;
int n;
#define NMAX 310
int num[NMAX];
int dst[NMAX];

struct edge {
	int f, t, w, n;
}E[NMAX*4];

int head[NMAX];
int cnt = 1;
void add(int f, int t, int w) {
	E[cnt].f = f, E[cnt].t = t, E[cnt].w = w, E[cnt].n = head[f];
	head[f] = cnt++;
}
void spfa(int s) {
	memset(dst, -0x3f, sizeof(dst));
	queue<int > Q;
	int inq[NMAX];
	memset(inq, 0, sizeof(inq));
	Q.push(s);
	dst[s] = 0;
	inq[s] = 1;
	while (!Q.empty()) {
		int s = Q.front();
		Q.pop();
		inq[s] = 0;
		for (int i = head[s]; i; i = E[i].n) {
			int d = E[i].t;
			if (dst[d] < dst[s] + E[i].w) {
				dst[d] = dst[s] + E[i].w;
				if (!inq[d]) {
					inq[d] = 1;
					Q.push(d);
				}
			}
		}
	}

}
int main() {
	cin >> n;
	for (int i = 1; i <= n; i++) {
		cin >> num[i];
	}
	memset(head, 0, sizeof(0));
	for (int i = 2; i < n ; i++) {
		add(i - 2, i + 1, 3 * num[i]);
		add(i + 1, i - 2, -3 * num[i] - 2);
	}
	add(0, 2, 2 * num[1]), add(2, 0, -num[1] * 2 - 1);
	add(n - 2, n, 2 * num[n]), add(n, n - 2, -2 * num[n] - 1);
	for (int i = 1; i <= n; i++) add(i - 1, i, 1); //不要忘记这个条件的添加
	/*for (int i = 1; i < cnt; i++) {
		printf("%d %d %d\n", E[i].f, E[i].t, E[i].w);
	}*/
	spfa(0);
	for (int i = 1; i <= n; i++) {
		if (i != 1) cout << " ";
		cout << dst[i] - dst[i - 1];
	}
	cout << endl;
}

例题2：
博客链接