public int MaxEnvelopes(int[,] envelopes)    {        if(envelopes == null || envelopes.Length == 0){    		return 0;    	}    	    	// 0. model the PRoblem    	var arr = new List<Doll>();    	var rowCount = envelopes.Length / 2;        	for (var i = 0;i < rowCount; i++){    		arr.Add(new Doll(envelopes[i,0], envelopes[i,1]));    	}    	    	// 1. sort the arrays     	arr = arr.OrderBy(x=>x).ToList();    	    	var result = new int[rowCount];    	for (var i = 0;i < rowCount; i++){    		// fetch the item from first to last    		result[i] = 1;    		for (var j = i-1;j >=0 ; j--){    			if(arr[i].Width > arr[j].Width && arr[i].Height > arr[j].Height){    				result[i] = Math.Max(result[i], result[j]+1);    			}    		}    	}    	//Console.WriteLine(result);    	var max = result.Max();    	    	return max;    	    }        public class Doll : IComparable    {    	public int Width;    	public int Height;    	public Doll(int width, int height){    		this.Width = width;    		this.Height = height;    	}    	    	public int CompareTo(object obj){    		var to = (Doll)obj;    		if(Width!=to.Width){    			return Width - to.Width;    		}else{    			return Height - to.Height;    		}    	}    }