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1、最小生成樹(MST樹)
針對(duì)連通圖;
(1)、現(xiàn)實(shí)意義:在n個(gè)城市之間建立通信網(wǎng)絡(luò),連通n個(gè)城市,只需要n-1條線路;
但是n個(gè)城市之間共有 n*(n-1)/2條路線,如何選擇n-1條,使我們花費(fèi)成本最小。
(2)、相同的一個(gè)圖形結(jié)構(gòu),有可能產(chǎn)生出不同形狀的生成樹,但是我們要找的是不同形狀生成樹里面耗費(fèi)最小的一棵樹;
(3)、研究的問題:怎樣從生成樹里面找到花費(fèi)代價(jià)最小的一顆,花費(fèi)最小,成本最低;耗費(fèi)代價(jià)最小的生成樹我們就稱之為:最小生成樹(MST樹)。
(4)、最小生成樹是不能有環(huán)形的;通過不同的方法,最終所找到的最小生成樹是相同的(在權(quán)值相同時(shí),有可能不一樣,但是權(quán)值最小是唯一的,肯定的)。
2、Kruskal算法思想
思想:每次找權(quán)值最小的邊,與頂點(diǎn)關(guān)系不大(不關(guān)注頂點(diǎn));
從邊的游離角度出發(fā),每次都要找權(quán)值路徑最小的邊,(特別注意看所選的邊是否購(gòu)成回路)
模型分析:
3、Kruskal算法實(shí)現(xiàn)
這里找最小代價(jià)cost時(shí),采用的是數(shù)組(調(diào)用系統(tǒng)快排),當(dāng)然用堆也可以。
均由C++代碼實(shí)現(xiàn)(用的是鄰接矩陣):
typedef struct MstEdge{ //最小生成樹的邊(弄成一個(gè)結(jié)構(gòu)體) int x; //row int y; //col int cost; }MstEdge; int cmp(const void *a, const void *b){ //快排比較的方法 return (*(MstEdge*)a).cost - (*(MstEdge*)b).cost; } bool isSame(int *father, int i, int j){ //判斷是否為回路,就是有相同的父節(jié)點(diǎn) while(father[i] != i){ i = father[i]; } while(father[j] != j){ j = father[j]; } return i == j; } void markSame(int *father, int i, int j){ //連通之后,標(biāo)記為有相同的父節(jié)點(diǎn) while(father[i] != i){ i = father[i]; } while(father[j] != j){ j = father[j]; } father[j] = i; } template<typename Type, typename E> void GraphMtx<Type, E>::MinSpanTree_Kruskal(){ int n = Graph<Type, E>::getCurVertex(); //由于要用到父類的保護(hù)數(shù)據(jù)或方法,有模板的存在,必須加上作用域限定符; MstEdge *edge1 = new MstEdge[n*(n-1)/2]; //最小生成樹的數(shù)組 int k = 0; for(int i = 0; i < n; i++){ for(int j = i+1; j < n; j++){ if(edge[i][j] != MAX_COST){ edge1[k].x = i; edge1[k].y = j; edge1[k].cost = edge[i][j]; k++; } } } qsort(edge1, k, sizeof(MstEdge), cmp); //調(diào)用系統(tǒng)的快排; int *father = new int[n]; //弄一個(gè)父節(jié)點(diǎn) Type v1, v2; for(i = 0; i < n; i++){ father[i] = i; //自己的父就是自己頂點(diǎn)的下標(biāo) } for(i = 0; i < n; i++){ if(!isSame(father, edge1[i].x, edge1[i].y)){ //父節(jié)點(diǎn)不相同 v1 = getValue(edge1[i].x); v2 = getValue(edge1[i].y); printf("%c-->%c : %d\n", v1, v2, edge1[i].cost); //找到了最小邊和cost markSame(father, edge1[i].x, edge1[i].y); //標(biāo)記為相同父節(jié)點(diǎn); } } }
4、完整代碼、測(cè)試代碼、測(cè)試結(jié)果
(1)、完整代碼
#ifndef _GRAPH_H_ #define _GRAPH_H_ #include<iostream> #include<queue> using namespace std; #define VERTEX_DEFAULT_SIZE 10 #define MAX_COST 0x7FFFFFFF template<typename Type, typename E> class Graph{ public: bool isEmpty()const{ return curVertices == 0; } bool isFull()const{ if(curVertices >= maxVertices || curEdges >= curVertices*(curVertices-1)/2) return true; //圖滿有2種情況:(1)、當(dāng)前頂點(diǎn)數(shù)超過了最大頂點(diǎn)數(shù),存放頂點(diǎn)的空間已滿 return false; //(2)、當(dāng)前頂點(diǎn)數(shù)并沒有滿,但是當(dāng)前頂點(diǎn)所能達(dá)到的邊數(shù)已滿 } int getCurVertex()const{ return curVertices; } int getCurEdge()const{ return curEdges; } public: virtual bool insertVertex(const Type &v) = 0; //插入頂點(diǎn) virtual bool insertEdge(const Type &v1, const Type &v2, E cost) = 0; //插入邊 virtual bool removeVertex(const Type &v) = 0; //刪除頂點(diǎn) virtual bool removeEdge(const Type &v1, const Type &v2) = 0; //刪除邊 virtual int getFirstNeighbor(const Type &v) = 0; //得到第一個(gè)相鄰頂點(diǎn) virtual int getNextNeighbor(const Type &v, const Type &w) = 0; //得到下一個(gè)相鄰頂點(diǎn) public: virtual int getVertexIndex(const Type &v)const = 0; //得到頂點(diǎn)下標(biāo) virtual void showGraph()const = 0; //顯示圖 virtual Type getValue(int index)const = 0; public: virtual void DFS(const Type &v) = 0; virtual void BFS(const Type &v) = 0; protected: int maxVertices; //最大頂點(diǎn)數(shù) int curVertices; //當(dāng)前頂點(diǎn)數(shù) int curEdges; //當(dāng)前邊數(shù) }; template<typename Type, typename E> class GraphMtx : public Graph<Type, E>{ //鄰接矩陣?yán)^承父類矩陣 #define maxVertices Graph<Type, E>::maxVertices //因?yàn)槭悄0?,所以用父類的?shù)據(jù)或方法都得加上作用域限定符 #define curVertices Graph<Type, E>::curVertices #define curEdges Graph<Type, E>::curEdges public: GraphMtx(int vertexSize = VERTEX_DEFAULT_SIZE){ //初始化鄰接矩陣 maxVertices = vertexSize > VERTEX_DEFAULT_SIZE ? vertexSize : VERTEX_DEFAULT_SIZE; vertexList = new Type[maxVertices]; //申請(qǐng)頂點(diǎn)空間 for(int i = 0; i < maxVertices; i++){ //都初始化為0 vertexList[i] = 0; } edge = new int*[maxVertices]; //申請(qǐng)邊的行 for(i = 0; i < maxVertices; i++){ //申請(qǐng)列空間 edge[i] = new int[maxVertices]; } for(i = 0; i < maxVertices; i++){ //賦初值為0 for(int j = 0; j < maxVertices; j++){ if(i != j){ edge[i][j] = MAX_COST; //初始化時(shí)都賦為到其它邊要花的代價(jià)為無窮大。 }else{ edge[i][j] = 0; //初始化時(shí)自己到自己認(rèn)為花費(fèi)為0 } } } curVertices = curEdges = 0; //當(dāng)前頂點(diǎn)和當(dāng)前邊數(shù) } GraphMtx(Type (*mt)[4], int sz){ //通過已有矩陣的初始化 int e = 0; //統(tǒng)計(jì)邊數(shù) maxVertices = sz > VERTEX_DEFAULT_SIZE ? sz : VERTEX_DEFAULT_SIZE; vertexList = new Type[maxVertices]; //申請(qǐng)頂點(diǎn)空間 for(int i = 0; i < maxVertices; i++){ //都初始化為0 vertexList[i] = 0; } edge = new int*[maxVertices]; //申請(qǐng)邊的行 for(i = 0; i < maxVertices; i++){ //申請(qǐng)列空間 edge[i] = new Type[maxVertices]; } for(i = 0; i < maxVertices; i++){ //賦初值為矩陣當(dāng)中的值 for(int j = 0; j < maxVertices; j++){ edge[i][j] = mt[i][j]; if(edge[i][j] != 0){ e++; //統(tǒng)計(jì)列的邊數(shù) } } } curVertices = sz; curEdges = e/2; } ~GraphMtx(){} public: bool insertVertex(const Type &v){ if(curVertices >= maxVertices){ return false; } vertexList[curVertices++] = v; return true; } bool insertEdge(const Type &v1, const Type &v2, E cost){ int maxEdges = curVertices*(curVertices-1)/2; if(curEdges >= maxEdges){ return false; } int v = getVertexIndex(v1); int w = getVertexIndex(v2); if(v==-1 || w==-1){ cout<<"edge no exit"<<endl; //要插入的頂點(diǎn)不存在,無法插入 return false; } if(edge[v][w] != MAX_COST){ //當(dāng)前邊已經(jīng)存在,不能進(jìn)行插入 return false; } edge[v][w] = edge[w][v] = cost; //因?yàn)槭菬o向圖,對(duì)稱, 權(quán)值賦為cost; return true; } //刪除頂點(diǎn)的高效方法 bool removeVertex(const Type &v){ int i = getVertexIndex(v); if(i == -1){ return false; } vertexList[i] = vertexList[curVertices-1]; int edgeCount = 0; for(int k = 0; k < curVertices; k++){ if(edge[i][k] != 0){ //統(tǒng)計(jì)刪除那行的邊數(shù) edgeCount++; } } //刪除行 for(int j = 0; j < curVertices; j++){ edge[i][j] = edge[curVertices-1][j]; } //刪除列 for(j = 0; j < curVertices; j++){ edge[j][i] = edge[j][curVertices-1]; } curVertices--; curEdges -= edgeCount; return true; } /* //刪除頂點(diǎn)用的是數(shù)組一個(gè)一個(gè)移動(dòng)的方法,效率太低。 bool removeVertex(const Type &v){ int i = getVertexIndex(v); if(i == -1){ return false; } for(int k = i; k < curVertices-1; ++k){ vertexList[k] = vertexList[k+1]; } int edgeCount = 0; for(int j = 0; j < curVertices; ++j){ if(edge[i][j] != 0) edgeCount++; } for(int k = i; k < curVertices-1; ++k) { for(int j = 0; j < curVertices; ++j) { edge[k][j] = edge[k+1][j]; } } for(int k = i; k < curVertices-1; ++k) { for(int j = 0; j < curVertices; ++j) { edge[j][k] = edge[j][k+1]; } } curVertices--; curEdges -= edgeCount; return true; } */ bool removeEdge(const Type &v1, const Type &v2){ int v = getVertexIndex(v1); int w = getVertexIndex(v2); if(v==-1 || w==-1){ //判斷要?jiǎng)h除的邊是否在當(dāng)前頂點(diǎn)內(nèi) return false; //頂點(diǎn)不存在 } if(edge[v][w] == 0){ //這個(gè)邊根本不存在,沒有必要?jiǎng)h return false; } edge[v][w] = edge[w][v] = 0; //刪除這個(gè)邊賦值為0,代表不存在; curEdges--; return true; } int getFirstNeighbor(const Type &v){ int i = getVertexIndex(v); if(i == -1){ return -1; } for(int col = 0; col < curVertices; col++){ if(edge[i][col] != 0){ return col; } } return -1; } int getNextNeighbor(const Type &v, const Type &w){ int i = getVertexIndex(v); int j = getVertexIndex(w); if(i==-1 || j==-1){ return -1; } for(int col = j+1; col < curVertices; col++){ if(edge[i][col] != 0){ return col; } } return -1; } public: void showGraph()const{ if(curVertices == 0){ cout<<"Nul Graph"<<endl; return; } for(int i = 0; i < curVertices; i++){ cout<<vertexList[i]<<" "; } cout<<endl; for(i = 0; i < curVertices; i++){ for(int j = 0; j < curVertices; j++){ if(edge[i][j] != MAX_COST){ cout<<edge[i][j]<<" "; }else{ cout<<"@ "; } } cout<<vertexList[i]<<endl; } } int getVertexIndex(const Type &v)const{ for(int i = 0; i < curVertices; i++){ if(vertexList[i] == v){ return i; } } return -1; } public: Type getValue(int index)const{ return vertexList[index]; } void DFS(const Type &v){ int n = Graph<Type, E>::getCurVertex(); bool *visit = new bool[n]; for(int i = 0; i < n; i++){ visit[i] = false; } DFS(v, visit); delete []visit; } void BFS(const Type &v){ int n = Graph<Type, E>::getCurVertex(); bool *visit = new bool[n]; for(int i = 0; i < n; i++){ visit[i] = false; } cout<<v<<"-->"; int index = getVertexIndex(v); visit[index] = true; queue<int> q; //隊(duì)列中存放的是頂點(diǎn)下標(biāo); q.push(index); int w; while(!q.empty()){ index = q.front(); q.pop(); w = getFirstNeighbor(getValue(index)); while(w != -1){ if(!visit[w]){ cout<<getValue(w)<<"-->"; visit[w] = true; q.push(w); } w = getNextNeighbor(getValue(index), getValue(w)); } } delete []visit; } public: void MinSpanTree_Kruskal(); protected: void DFS(const Type &v, bool *visit){ cout<<v<<"-->"; int index = getVertexIndex(v); visit[index] = true; int w = getFirstNeighbor(v); while(w != -1){ if(!visit[w]){ DFS(getValue(w), visit); } w = getNextNeighbor(v, getValue(w)); } } private: Type *vertexList; //存放頂點(diǎn)的數(shù)組 int **edge; //存放邊關(guān)系的矩陣 }; ////////////////////////////////////////////////////////////////////////////////////////////////////// typedef struct MstEdge{ int x; //row int y; //col int cost; }MstEdge; int cmp(const void *a, const void *b){ return (*(MstEdge*)a).cost - (*(MstEdge*)b).cost; } bool isSame(int *father, int i, int j){ while(father[i] != i){ i = father[i]; } while(father[j] != j){ j = father[j]; } return i == j; } void markSame(int *father, int i, int j){ while(father[i] != i){ i = father[i]; } while(father[j] != j){ j = father[j]; } father[j] = i; } template<typename Type, typename E> void GraphMtx<Type, E>::MinSpanTree_Kruskal(){ int n = Graph<Type, E>::getCurVertex(); //由于要用到父類的保護(hù)數(shù)據(jù)或方法,有模板的存在,必須加上作用域限定符; MstEdge *edge1 = new MstEdge[n*(n-1)/2]; int k = 0; for(int i = 0; i < n; i++){ for(int j = i+1; j < n; j++){ if(edge[i][j] != MAX_COST){ edge1[k].x = i; edge1[k].y = j; edge1[k].cost = edge[i][j]; k++; } } } qsort(edge1, k, sizeof(MstEdge), cmp); int *father = new int[n]; Type v1, v2; for(i = 0; i < n; i++){ father[i] = i; } for(i = 0; i < n; i++){ if(!isSame(father, edge1[i].x, edge1[i].y)){ v1 = getValue(edge1[i].x); v2 = getValue(edge1[i].y); printf("%c-->%c : %d\n", v1, v2, edge1[i].cost); markSame(father, edge1[i].x, edge1[i].y); } } } #endif
(2)、測(cè)試代碼
#include"Graph2.h" int main(void){ GraphMtx<char,int> gm; gm.insertVertex('A'); //0 gm.insertVertex('B'); //1 gm.insertVertex('C'); //2 gm.insertVertex('D'); //3 gm.insertVertex('E'); //4 gm.insertVertex('F'); //5 gm.insertEdge('A','B',6); gm.insertEdge('A','C',1); gm.insertEdge('A','D',5); gm.insertEdge('B','C',5); gm.insertEdge('B','E',3); gm.insertEdge('C','E',6); gm.insertEdge('C','D',5); gm.insertEdge('C','F',4); gm.insertEdge('D','F',2); gm.insertEdge('E','F',6); gm.showGraph(); gm.MinSpanTree_Kruskal(); return 0; }
(3)、測(cè)試結(jié)果
測(cè)試圖模型
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