42题 Maximum Subarray II 最大子数组 II

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本文介绍了一种解决最大子数组问题的改进方法，通过双重动态规划寻找数组中两个非重叠且和最大的子数组。算法详细解释了如何计算左边界最大子数组和右边界最大子数组，并最终找出两者相加的最大值。

Maximum Subarray II最大子数组 II

Description
Given an array of integers, find two non-overlapping subarrays which have the largest sum. The number in each subarray should be contiguous. Return the largest sum.

public class Solution {
    /*
     * @param nums: A list of integers
     * @return: An integer denotes the sum of max two non-overlapping subarrays
     */
    public int maxTwoSubArrays(List<Integer> nums) {
        // write your code here
        if(nums == null){
          return 0 ;
        }
        int size = nums.size() ;
        int[] left = new int[size] ;
        int[] right = new int[size] ;
        int sum = 0 ;
        int max = Integer.MIN_VALUE ;
        for(int i = 0 ; i < size ; i++){
           sum = sum + nums.get(i) ;
           max = Math.max(sum , max) ;
           sum = Math.max(0 , sum) ;
           left[i] = max ; 
        }
         sum = 0 ;
         max = Integer.MIN_VALUE ;
        for(int i = size-1 ; i >= 0 ; i--){
           sum = sum + nums.get(i) ;
           max = Math.max(sum , max) ;
           sum = Math.max(0 , sum) ;
           right[i] = max ; 
        }
       
         max = Integer.MIN_VALUE ;
        for(int i =0 ; i < size-1 ; i++){
          max = Math.max(max , left[i]+right[i+1]);
        }
         return max ;
    }
}