【图论】关键路径求法c++
代码结构如下图：
其中topologicalSort(float**, int, int*, bool*, int, int)用来递归求解拓扑排序，topologicalSort(float**, int*&, int, int, int)传参图的邻接矩阵mat与结点个数n，与一个引用变量数组topo，返回一个布尔值表示该图是否存在拓扑排序，同时将引用变量数组topo赋值为该图的拓扑序列。
getEdges(float**, int**&, int)传参图的邻接矩阵mat，引用变量二维数组edge，结点数n。然后将返回该图的边数，同时将float赋值为一个存储图的边的起点与终点的edgeNum * 2维的数组。
aoe(float**, int, int*&, int&, float*&, float*&, float*&, float*&, int*&, int**&, int&)分别传参邻接矩阵mat，结点数n，引用变量criticalPath表示关键路径，引用变量ve，vl，e，l正如名字所示，topo与edges表示拓扑序列与边，edgeNum表示边的数量。
aoe(float**, int, int*&, int&, float*&, float*&, float*&, float*&)与上一个函数差不多，只是少了topo与edges，edgeNum两个参数，并且多了一个布尔类型的返回值，返回的是关键路径是否存在。
aoe(float**, int*&, int&)则更是只有三个参数，他不对ve，vl，e，l进行返回。
aoe
static const float INF = 1.0f/0.0f;
// x is what you are, and y is meaning to you are the no.y numbers to sort.
void topologicalSort(float** mat, int n, int* arr, bool* flags, int x=0, int y=0) {
arr[y] = x;
flags[x] = true;
float tmp[n];
// first, set all the elements of the no.x row to INF, and store the original value to tmp;
// just like delete this vertex
for (int i = 0; i < n; ++i) {
tmp[i] = mat[x][i];
mat[x][i] = INF;
}
for (int i = 0; i < n; ++i) {
int k = (x + i) % n;
// if k have not recorded in arr.
if (!flags[k]) {
bool flag = true;
// this loop is aim to find a vertex whose in_degree is equals to 0.
for (int j = 0; j < n; ++j) {
if (j != k && mat[j][k] != INF) {
flag = false;
break;
}
}
// if you delete x, the in_degree of k is equals to 0. so do a recursive call.
if (flag) {
topologicalSort(mat, n, arr, flags, k, y+1);
}
}
}
// restore the no.x row
for (int i = 0; i < n; ++i) {
mat[x][i] = tmp[i];
}
}
bool topologicalSort(float** mat, int* &topo, int n, int x=0, int y=0) {
topo = new int[n];
bool *flags = new bool[n];
for (int i = 0; i < n; ++i) {
flags[i] = false;
}
topologicalSort(mat, n, topo, flags, x, y);
for (int i = 0; i < n; ++i) {
if (!flags[i]) return false;
}
return true;
}
int getEdges(float** mat, int** &edges, int n) {
// e is for the edges, whose account is unsure
// ans is for the number of edges
int ans = 0;
int** e = new int*[n * (n - 1)];
for (int i = 0; i < n; ++i) {
for (int j = 0; j < n; ++j) {
if (i == j || mat[i][j] == INF) continue;
e[ans++] = new int[]{i, j};
}
}
// copy e into edges
edges = new int*[ans];
for (int i = 0; i < ans; ++i) {
edges[i] = e[i];
}
delete[] e;
return ans;
}
void aoe(float** mat, int n, int* &criticalPath, int &length, float* &ve, float* &vl, float* &e, float* &l, int* &topo, int** &edges, int &edgeNum) {
ve = new float[n];
vl = new float[n];
e = new float[edgeNum];
l = new float[edgeNum];
for (int i = 0; i < n; ++i) {
ve[i] = 0;
}
for (int i = 1; i < n; ++i) {
int max = i;
for (int j = 0; j < i; ++j) {
if (mat[topo[j]][topo[i]] == 0 || mat[topo[j]][topo[i]] == INF) continue;
if (ve[topo[j]] + mat[topo[j]][topo[i]] > ve[topo[max]] + mat[topo[max]][topo[i]]) {
max = j;
}
}
ve[topo[i]] = ve[topo[max]] + mat[topo[max]][topo[i]];
}
for (int i = 0; i < n; ++i) {
vl[i] = ve[topo[n - 1]];
}
for (int i = n - 2; i >= 0; --i) {
int min = i;
for (int j = i + 1; j < n; ++j) {
if (mat[topo[i]][topo[j]] == 0 || mat[topo[i]][topo[j]] == INF) continue;
if (vl[topo[j]] - mat[topo[i]][topo[j]] < vl[topo[min]] - mat[topo[i]][topo[min]]) {
min = j;
}
}
vl[topo[i]] = vl[topo[min]] - mat[topo[i]][topo[min]];
}
for (int i = 0; i < edgeNum; ++i) {
e[i] = ve[edges[i][0]];
l[i] = vl[edges[i][1]] - mat[edges[i][0]][edges[i][1]];
}
int* critical = new int[n];
critical[0] = topo[0];
length = 1;
for (int i = 0; i < n; ++i) {
critical[i] = -1;
}
for (int i = 0; i < edgeNum; ++i) {
float le = l[i] - e[i];
if (le < 1e-32) {
critical[edges[i][0]] = edges[i][1];
length++;
}
}
criticalPath = new int[length];
int p = 0;
int q = 0;
while (p != -1) {
criticalPath[q++] = p;
p = critical[p];
}
delete[] critical;
}
bool aoe(float** mat, int n, int* &criticalPath, int &length, float* &ve, float* &vl, float* &e, float* &l) {
int* topo;
int flag = topologicalSort(mat, topo, n);
if (!flag) return false;
int** edges;
int edgeNum = getEdges(mat, edges, n);
aoe(mat, n, criticalPath, length, ve, vl, e, l, topo, edges, edgeNum);
return true;
}
bool aoe(float** mat, int n, int* &criticalPath, int &length) {
float* ve;
float* vl;
float* e;
float* l;
return aoe(mat, n, criticalPath, length, ve, vl, e, l);
}
在main函数中进行一个测试，传参如下图：
2
3
5
3
9
6
4
2
3
v1
v2
v3
v4
v5
v6
int main() {
int n = 6;
float** mat = new float*[] {
new float[] {0, 2, 3, INF, INF, INF },
new float[] {INF, 0, INF, 5, INF, INF },
new float[] {INF, 3, 0, 9, 4, INF },
new float[] {INF, INF, INF, 0, 6, 2 },
new float[] {INF, INF, INF, INF, 0, 3 },
new float[] {INF, INF, INF, INF, INF, 0 }
};
char** value = new char*[n]{
"v1", "v2", "v3", "v4", "v5", "v6"
};
float *ve, *vl, *e, *l;
int* criticalPath;
int length;
int** edges;
int* topo;
topologicalSort(mat, topo, n);
int edgeNum = getEdges(mat, edges, n);
aoe(mat, n, criticalPath, length, ve, vl, e, l);
cout << "拓扑排序为：";
for (int i = 0; i < n; ++i) {
cout << value[topo[i]] << " ";
}
cout << "\n\n";
cout << "共有" << edgeNum << "条边：\n";
for (int i = 0; i < edgeNum; ++i) {
cout << value[edges[i][0]] << "->" << value[edges[i][1]] << ": " << mat[edges[i][0]][edges[i][1]] << endl;
}
cout << endl;
for (int i = 0; i < n; ++i) {
cout << '\t' << value[i];
}
cout << endl;
cout << "ve:";
for (int i = 0; i < n; ++i) {
cout << '\t' << ve[i];
}
cout << endl;
cout << "vl:";
for (int i = 0; i < n; ++i) {
cout << '\t' << vl[i];
}
cout << "\n\n";
for (int i = 0; i < edgeNum; ++i) {
cout << '\t' << value[edges[i][0]] << "->" << value[edges[i][1]];
}
cout << endl;
cout << "e:";
for (int i = 0; i < edgeNum; ++i) {
cout << '\t' << e[i];
}
cout << endl;
cout << "l:";
for (int i = 0; i < edgeNum; ++i) {
cout << '\t' << l[i];
}
cout << endl;
cout << "l-e:";
for (int i = 0; i < edgeNum; ++i) {
cout << '\t' << l[i] - e[i];
}
cout << "\n\n";
cout << "关键路径为：";
for (int i = 0; i < length; ++i) {
cout << value[criticalPath[i]] << " ";
}
return 0;
}
运行结果如下：
