最近在学算法,沉迷于js的我,就想用js敲一敲这个prim算法,至于prim算法具体是什么,怎么回事,大家可以自行搜索,这里只贴上代码和部分注解
数据是从文件里读出来的所以用了一下node.js,数据格式如下
7 9
1 2 28
1 6 10
2 7 14
2 3 16
6 5 25
7 5 24
7 4 18
3 4 12
5 4 22
var fs = require('fs')
var path = require('path');
var Q = require("q");
var MAX = 100000;
var dingdian;//顶点数
var bian;//边数
var edge = [];//矩阵
var node = [] // 记录节点
var addNew = []; //设置顶点是否加入到集合
// 优先队列数据结构
function PriorityQueue() {
var items = [];
function QueueElement (element, priority){ // {1}
this.element = element;
this.priority = priority;
}
this.enqueue = function(element, priority){
var queueElement = new QueueElement(element, priority);
var added = false;
for (var i=0; i< items.length; i++){
if (queueElement.priority < items[i].priority){ // {2}
items.splice(i,0,queueElement); // {3}
added = true;
break; // {4}
}
}
if (!added){
items.push(queueElement); //{5}
}
};
this.dequeue = function(){
return items.shift();
};
this.front = function(){
return items[0];
};
this.isEmpty = function(){
return items.length == 0;
};
this.size = function(){
return items.length;
};
}
var q = new PriorityQueue(); //创建优先队列
//初始化输入矩阵
function initRect(length) {
for(var i = 1; i<length+1; i++) {
edge[i] = [];
for(var j=1; j<length+1;j++) {
edge[i][j] = MAX;
}
}
}
//读取数据
function preadFile (file){
var deferred = Q.defer();
fs.readFile(file,'utf-8', function(err,data){
if(!err){
deferred.resolve(data);
}else{
deferred.reject(err);
}
});
return deferred.promise;
}
var filein = path.resolve('input.txt')
preadFile(filein).then(function(data){
var arr = data.split(/\r\n/) //回车空行分割读取
// console.log(arr)
for(var i=0;i<arr.length;i++) {
var _arr = arr[i].split(' ');
if(_arr.length === 2) {
dingdian = parseInt(_arr[0]);
bian = parseInt(_arr[1])
initRect(dingdian);//进行初始化
}else if(_arr.length === 3) { //添加数据到矩阵
edge[_arr[0]][_arr[1]] = parseInt(_arr[2]);
edge[_arr[1]][_arr[0]] = parseInt(_arr[2]);
}else {
return;
}
}
//求值
var result = prim(dingdian, edge);
var _arr = [];
for(key in result) {
_arr[key] = result[key].priority
}
_arr.splice(0,1);
var max = Math.max.apply(Math, _arr)
console.log(max)//结果是25
});
// 开始prim算法 prim([顶点数],[矩阵])
function prim(dingdian, edge) {
for(var i=1; i<dingdian+1; i++) {
node[i] = {}
node[i].element = i;
node[i].priority = MAX;
addNew[i] = false; //把所有点都设置成没有放入
}
// console.log('node',node[1])
node[1].priority = 0; //从起始点开始找
q.enqueue(node[1].element, node[1].priority)//把权最小的放入队列
while(!q.isEmpty()) {
var _q = q.front();
q.dequeue();
var flag = _q.element;//
if(addNew[flag]) {
continue;
}
addNew[flag] = true;
for(var j=1; j<dingdian+1; j++) {
if(j!=flag && !addNew[j] && node[j].priority > edge[flag][j]){
node[j].priority = edge[flag][j];
q.enqueue(node[j].element, node[j].priority)
}
}
}
return node
}