js神秘的电报密码---哈弗曼编码

Posted 2020-12-26

 

 

 

 哈夫曼编码，根据每个单词在文本中出现的次数频率为权值，频率高的权值大。然后每次取两个频率最小的生成树，最后生成一颗大树。从根节点到该单词的路径，左边为0，右边为1,

		function HFM(){
			var souce = [];
			
			function createNode(node){
				var obj = {
					weight:0,  
					parent:-1,
					lchild:-1,
					rchild:-1,
					value:\'\'
				};
				
				return Object.assign(obj,node);
			}
			
			this.addNode = function(node){
				//添加单词和频率（权值）
				souce.push(createNode(node));
			}
			
			this.createTree = function(){
				//哈夫曼树
				var HuffNode  = JSON.parse(JSON.stringify(souce));
				var n = HuffNode.length;
				
				var x1,x2; //两个权值最小的索引 
				var m1,m2;         //两个权值最小的值
				
				for(var i = 0; i < n ; i++){
					m1 = m2 = Infinity;  //初始化为最大值
					x1 = x2 = -1; 
					
					for(var j = 0; j < n+i; j++){ //寻找两个权值最小，且父节点为-1的
						var item = HuffNode[j];
						if(item.weight  < m1 && item.parent == -1){
							m2 = m1;
							x2 = x1;
							
							m1 = item.weight;
							x1 = j;
							
						}else if(item.weight  < m2 && item.parent == -1){
							m2 = item.weight;;
							x2 = j;
						}
					}
					
					if(x1 != -1 && x2 != -1){
						HuffNode[x1].parent = n + i;  //更新父节点
						HuffNode[x2].parent = n + i;
						
						//创建一个新的节点
						HuffNode[n+i] = createNode({
							weight:m1+m2,
							lchild:x1,
							rchild:x2
						});
					}
					
					
				}
				
				return HuffNode;
			};
			
			this.getCode = function(){
				//哈夫曼编码
				var n = souce.length; 
				var tree = this.createTree();
				var codes = {};
				for(var i = 0; i < n; i++){
					var p = tree[i].parent;
					var code = \'\';
					var c = i;
					while(p != -1){  //迭代前溯
						if(tree[p].lchild == c){
							code = 0 + code;
						}else{
							code = 1 + code;
						}
						c = p;
						p = tree[p].parent;
					}
					
					codes[ tree[i].value ] = code;
					console.log(tree[i].value , code);
				
				}
				
				return codes;
			}
			
			
		}
		
		var hfm = new HFM();
		
		hfm.addNode({
			weight:5,
			value:"a"
		});
		hfm.addNode({
			weight:32,
			value:"b"
		});
		hfm.addNode({
			weight:18,
			value:"c"
		});
	    hfm.addNode({
			weight:7,
			value:"d"
		});
		hfm.addNode({
			weight:25,
			value:"e"
		});
		hfm.addNode({
			weight:13,
			value:"f"
		});
		
		console.log(hfm.getCode())