LeetCode-321. Create Maximum Number

Given two arrays of length m and n with digits 0-9 representing two numbers. Create the maximum number of length k <= m + n from digits of the two. The relative order of the digits from the same array must be preserved. Return an array of the k digits. You should try to optimize your time and space complexity.

Example 1:

nums1 = [3, 4, 6, 5]
nums2 = [9, 1, 2, 5, 8, 3]
k = 5
return [9, 8, 6, 5, 3]

Example 2:

nums1 = [6, 7]
nums2 = [6, 0, 4]
k = 5
return [6, 7, 6, 0, 4]

Example 3:

nums1 = [3, 9]
nums2 = [8, 9]
k = 3

return [9, 8, 9]   

这一题挺难的，我用的最慢的方法~将k分成两部分，首先从第一个数组里取i个可以组成最大i位数的数，然后从第二个数组里取k-i个可以组成最大数的数，然后组合起来成一个最大的数，i从最小到最大遍历一次，从而求得最大的数。当然很慢了，我看tags里是用动态规划或贪婪算法的。不过我去大家的博客里看了看，都是这种方法~那就酱紫吧~

import java.math.BigInteger;
public class Solution {
     public int[] maxNumber(int[] nums1, int[] nums2, int k) {
    	int len1 = nums1.length;
        int len2 = nums2.length;
        int i = k;
        BigInteger max = BigInteger.ZERO;
        if(k>len1){
        	i = len1;
        }
    	for(; i >= 0 && k-i<=len2; i--){
        	int[] num1 = calmaxnum(nums1,i);
        	int[] num2 = calmaxnum(nums2,k-i);
        	BigInteger maxnum = totalmaxnum(num1,num2);
        	if(maxnum.compareTo(max)>0){
        		max = maxnum;
        	}
        	
        }
    	int[] ans = convertToArray(max);
    	return ans;
    	
    	
    	
    }
    
   int[]  calmaxnum(int[] num,int k){
    	int[] ans = new int[k];
    	int len = num.length;
    	int index = 0;
    	for(int i = 0; i < k; i++){
    		int[] ans2= findmaxnum(num,index,len-k+i+1);
    		ans[i] = ans2[0];
    		index = ans2[1]+1;
    	}
    	
    	return ans;
    }
    
   int[]  findmaxnum(int[] num,int left,int right){
    	int max = num[left];
	   //int max = 0;
    	int index = left;
    	for(int i = left;i<right;i++){
    		if(num[i]>max){
    			max = num[i];
    			index = i;
    		}
    	}
    	int[] ans = {max , index};
    	return ans;
    }
    
   BigInteger totalmaxnum(int[] num1, int[] num2){
    	int len1 = num1.length;
    	int len2 = num2.length;
    	int index1 = 0;
    	int index2 = 0;
    	String str = "";
    	for(int i = 0; i<len1+len2; i++){
    		if(index1>=len1){
    			str += num2[index2++];
    		}else if(index2 >= len2){
    			str += num1[index1++];
    		}else if(num1[index1]>num2[index2]){
    			str += num1[index1++];
    		}else if(num1[index1]<num2[index2]){
    			str += num2[index2++];
    		}else{
    			int tempindex1 = index1;
    			int tempindex2 = index2;
    			while(true){
    				tempindex1++;
    				tempindex2++;
    				if(tempindex1 >=len1){
    	    			str += num2[index2++];
    	    			break;
    	    		}else if(tempindex2 >= len2){
    	    			str += num1[index1++];
    	    			break;
    	    		}else if(num1[tempindex1]>num2[tempindex2]){
    	    			str += num1[index1++];
    	    			break;
    	    		}else if(num1[tempindex1]<num2[tempindex2]){
    	    			str += num2[index2++];
    	    			break;
    	    		}
    			}
    			
    		}
    	}
    	BigInteger ans = new BigInteger(str);
    	return ans;
    }
    
    int[] convertToArray(BigInteger max){
    	String str = ""+max;
    	int len = str.length();
    	int[] ans = new int[len];
    	for(int i = len-1; i>=0; i--){
    		ans[i] = (max.remainder(BigInteger.valueOf(10))).intValue();
    		max = max.divide(BigInteger.valueOf(10));
    	}
    	
    	return ans;
    }
}