算法实践篇-求最大子数组

package com.sort.divid;

/**
 * 求最大子数组
 * @author Administrator
 *nlogn
 */
public class MaxSubArray {
	private static int[] findMaxCrossSubArray(int [] data,int left,int middle,int right){
		int [] result=new int[3];
		int leftmax=data[middle];
		int sum=leftmax;
		int leftIndex=middle;
		for(int i=middle-1;i>=left;i--){
			sum=sum+data[i];
			if(sum>leftmax){
				leftmax=sum;
				leftIndex=i;
			}
		}
		int rightmax=data[middle+1];
		sum=rightmax;
		int rightIndex=middle+1;
		for(int i=middle+2;i<=right;i++){
			sum=sum+data[i];
			if(sum>rightmax){
				rightmax=sum;
				rightIndex=i;
			}
		}
		result[0]=leftmax+rightmax;
		result[1]=leftIndex;
		result[2]=rightIndex; 
		return result;
	}
	
	private static int[] findMaxSubArray(int []data,int left,int right){
		int [] result=new int[3];
		if(left==right){
			result[0]=data[left];
			result[1]=left;
			result[2]=right;
			return result;
		}
		int middle=(left+right)/2;
		int[] leftResult=findMaxSubArray(data,left,middle);
		int [] rightResult=findMaxSubArray(data,middle+1,right);
		int []crossResult=findMaxCrossSubArray(data,left,middle,right);
		if(leftResult[0]>rightResult[0]&&leftResult[0]>crossResult[0]){
			return leftResult;
		}else if(rightResult[0]>leftResult[0]&&rightResult[0]>crossResult[0]){
			return rightResult;
		}else{
			return crossResult;
		}
	}

	public static void main(String[] args) {
		int[] data=new int[]{-1,2,9,11,-20,9,6,22,-8,9,1};
		for(int i=0;i<data.length;i++){
			System.out.print(data[i]+" ");
		}
		System.out.println();
		int []result=findMaxSubArray(data,0,data.length-1);;
		for(int i=0;i<result.length;i++){
			System.out.print(result[i]+" ");
		}
		System.out.println();

	}

}