关于差分约束（转载）

（本文假设读者已经有以下知识：最短路径的基本性质、Bellman-Ford算法。）比如有这样一组不等式：

$$ \begin{cases} X1 - X2 <= 0 \\\\ X1 - X5 <= (-1) \\\\ X2 - X5 <= 1 \\\\ X3 - X1 <= 5 \\\\ X4 - X1 <= 4 \\\\ X4 - X3 <= (-1) \\\\ X5 - X3 <= (-3) \\\\ X5 - X4 <= (-3) \end{cases} $$