GraphMatrix：：DFS深度优先搜索

template <typename Tv, typename Te> //深度优先搜索DFS算法（全图）
void Graph<Tv, Te>::dfs(int s) { //assert: 0 <= s < n
reset(); int clock = 0; int v = s; //初始化
do //逐一检查所有顶点
if (UNDISCOVERED == status(v)) //一旦遇到尚未发现的顶点
DFS(v, clock); //即从该顶点出发启动一次DFS
while (s != (v = (++v % n))); //按序号检查，故不漏不重
}

template <typename Tv, typename Te> //深度优先搜索DFS算法（单个连通域）
void Graph<Tv, Te>::DFS(int v, int& clock) { //assert: 0 <= v < n
dTime(v) = ++clock; status(v) = DISCOVERED; //发现当前顶点v
for (int u = firstNbr(v); -1 < u; u = nextNbr(v, u)) //枚举v的所有邻居u
switch (status(u)) { //并视其状态分别处理
case UNDISCOVERED: //u尚未发现，意味着支撑树可在此拓展
status(v, u) = TREE; parent(u) = v; DFS(u, clock); break;
case DISCOVERED: //u已被发现但尚未访问完毕，应属被后代指向的祖先
status(v, u) = BACKWARD; break;
default: //u已访问完毕（VISITED，有向图），则视承袭关系分为前向边或跨边
status(v, u) = (dTime(v) < dTime(u)) ? FORWARD : CROSS; break;
}
status(v) = VISITED; fTime(v) = ++clock; //至此，当前顶点v方告访问完毕
}