最大子序列和问题--时间复杂度O（NlogN)

package a;
/*
 * 最大子序列和问题，时间复杂度O（NlogN)
 */
public class Sequence {
    private static int maxSumRec(int[] a,int left,int right ){
        if(left==right)
            if(a[left]>0)
                return a[left];
            else 
                return 0;
        int center=(left+right)/2;
        int maxLeftSum =maxSumRec(a,left,center);//递归求前部分最大值
        int maxRightSum = maxSumRec(a,center+1,right);//递归求后部分最大值
        //求前半部分含最后一个元素的最大值
        int maxLeftBorderSum=0,leftBorderSum=0;
        for(int i=center;i>=left;i--){
            leftBorderSum+=a[i];
            if(leftBorderSum>maxLeftBorderSum)
                maxLeftBorderSum=leftBorderSum;
        }
        //求后半部分含第一个元素的最大值
        int maxRightBorderSum=0,rightBorderSum=0;
        for(int i=center+1;i<=right;i++){
            rightBorderSum+=a[i];
            if(rightBorderSum>maxRightBorderSum)
                maxRightBorderSum=rightBorderSum;
        }
        
        return max3(maxLeftSum,maxRightSum,maxLeftBorderSum+maxRightBorderSum);
    }
    //求最大值
    private static int max3(int maxLeftSum, int maxRightSum, int q) {
        // TODO Auto-generated method stub
        int max;
        if(maxLeftSum>maxRightSum)
            max=maxLeftSum;
        else
            max=maxRightSum;
        if(q>max)
            max=q;
        return max;
    }
    
    public static void main(String[] args){
        int[] a={4,-3,5,-2,-1,2,6,-2};
        System.out.println(maxSumRec(a, 0, a.length-1));
    }
}