java遞歸解決最大子數組問題（算法導論4.1）

基本按照書上的流程實作了遞歸解決最大子數組問題，複雜度為O（nlgn）

package 最大子數組4_1;

public class Solution {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		int[] arr = new int[] {13,-3,-25,20,-3,-16,-23,18,20,-7,12,-5,-22,15,-4};
		int[] result = new int[3];
		System.out.println(findMaxSubArray(arr, 0, arr.length-1)[2]);
	}
	static int[] findCrossMax(int[] arr, int low,int mid,int high) {
		if(low == high) {
			return new int[] {low,high,arr[low]};
		}
		int leftIndex = mid,rightIndex = mid +1;
		int sum = 0;
		int leftSum = Integer.MIN_VALUE, rightSum = Integer.MIN_VALUE;
		for(int i = mid;i>=low;i--) {
			sum = sum + arr[i];
			if(sum > leftSum) {
				leftSum = sum;
				leftIndex = i;
			}
		}
		sum = 0;
		for(int i = mid+1;i <= high; i++) {
			sum = sum + arr[i];
			if(sum > rightSum) {
				rightSum = sum;
				rightIndex = i;
			}
		}
		return new int[] {leftIndex,rightIndex,leftSum + rightSum};
	}
	
	static int[] findMaxSubArray(int[] arr, int low,int high) {
		if(low == high) {
			return new int[]{low,high,arr[low]};
		}
		int mid = (low + high) /2;
		int[] resultLeft,resultRight,resultCross = new int[3];
		resultLeft = findMaxSubArray(arr, low, mid);
		resultRight = findMaxSubArray(arr, mid+1, high);
		resultCross = findCrossMax(arr, low, mid, high);
		if(resultLeft[2] > resultCross[2] && resultLeft[2] > resultRight[2]) {
			return resultLeft;
		}
		else
			return resultCross[2] > resultRight[2]? resultCross:resultRight;
	}

}