Russian Doll Envelopes

题目描述：

You have a number of envelopes with widths and heights given as a pair of integers (w, h). One envelope can fit into another if and only if both the width and height of one envelope is greater than the width and height of the other envelope.

What is the maximum number of envelopes can you Russian doll? (put one inside other)

Example:
Given envelopes = [[5,4],[6,4],[6,7],[2,3]], the maximum number of envelopes you can Russian doll is 3 ([2,3] => [5,4] => [6,7]).

public class Solution {
    public int maxEnvelopes(int[][] envelopes) {
        int n=envelopes.length;
        if(n==0)
        	return 0;
        Arrays.sort(envelopes, new Comparator<int[]>(){
            public int compare(int[] arr1, int[] arr2){
                if(arr1[0] == arr2[0])
                    return arr1[1] - arr2[1];
                else
                    return arr1[0] - arr2[0];
           } 
        });
		int max=0;
		boolean[] started=new boolean[envelopes.length];
		for(int i=0;i<n;i++){
			if(!started[i]){
				max=max>getMaxEnvelopes(envelopes, i, started)?max:getMaxEnvelopes(envelopes, i, started);
			}
		}
		return max;
    }
	
	public int getMaxEnvelopes(int[][] envelopes,int startIndex,boolean[] started){
		int max=1;
		int width=envelopes[startIndex][0];
		int height=envelopes[startIndex][1];
		for(int i=startIndex+1;i<envelopes.length;i++){
			if(envelopes[i][0]>width&&envelopes[i][1]>height){
				started[i]=true;
				int num=getMaxEnvelopes(envelopes, i , started)+1;
				max=max>num?max:num;
			}
		}
		return max;
	}
}

public class Solution {
    public int maxEnvelopes(int[][] envelopes) {
	    if(envelopes == null || envelopes.length == 0 
	       || envelopes[0] == null || envelopes[0].length != 2)
	        return 0;
	    Arrays.sort(envelopes, new Comparator<int[]>(){
	        public int compare(int[] arr1, int[] arr2){
	            if(arr1[0] == arr2[0])
	                return arr2[1] - arr1[1];
	            else
	                return arr1[0] - arr2[0];
	       } 
	    });
	    int dp[] = new int[envelopes.length];
	    int len = 0;
	    for(int[] envelope : envelopes){
	        int index = Arrays.binarySearch(dp, 0, len, envelope[1]);
	        if(index < 0)
	            index = -(index + 1);
	        dp[index] = envelope[1];
	        if(index == len)
	            len++;
	    }
	    return len;
	}
}

最后

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