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Maximum Subarray Ii

Maximum Subarray Ii

题目地址

题目描述

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.

代码

Approach #1

public class Solution {
public int maxTwoSubArray(ArrayList<Integer> nums) {
if (nums == null || nums.isEmpty()) return -1;
int size = nums.size();
int[] maxSubArrayFront = new int[size];
forwardTraversal(nums, maxSubArrayFront);
​
int[] maxSubArrayBack = new int[size];
backwardTraversal(nums, maxSubArrayBack);
​
int maxTwoSub = Integer.MIN_VALUE;
for (int i = 0; i < size - 1; i++) {
maxTwoSub = Math.max(maxTwoSub, maxSubArrayFront[i] + maxSubArrayBack[i + 1]);
}
​
return maxTwoSub;
}
​
private void forwardTraversal(List<Integer> nums, int[] maxSubArray) {
int sum = 0, minSum = 0, maxSub = Integer.MIN_VALUE;
int size = nums.size();
for (int i = 0; i < size; i++) {
minSum = Math.min(minSum, sum);
sum += nums.get(i);
maxSub = Math.max(maxSub, sum - minSum);
maxSubArray[i] = maxSub;
}
}
​
private void backwardTraversal(List<Integer> nums, int[] maxSubArray) {
int sum = 0, minSum = 0, maxSub = Integer.MIN_VALUE;
int size = nums.size();
for (int i = size - 1; i >= 0; i--) {
minSum = Math.min(minSum, sum);
sum += nums.get(i);
maxSub = Math.max(maxSub, sum - minSum);
maxSubArray[i] = maxSub;
}
}
​
}