最大子数组问题

   
public static int (int []a){
	int max=0;
	int sum=0;
	for(int i=0;i<a.length;i++){
		for(int j=i;j<a.length;j++){
			for(int k=i;k<=j;k++){
				sum+=a[k];
			}
			if(sum>max){
				max=sum;
			}
			sum=0;
		}
	}
	return max;
}

   //采用分治策略，时间复杂度为O(nlgn)
public static int getMaxSum2(int []a){
	return findMaxSub(a,0,a.length-1);
}
public static 大专栏  最大子数组问题">int findMaxSub(int[] a,int left,int right){
	if(left==right) return a[left];
	int mid=left+(right-left)/2;
	int leftSum=findMaxSub(a, left, mid);
	int midSum=findMaxCro(a, left,mid, right);
	int rightSum=findMaxSub(a, mid+1, right);
	if(leftSum>midSum&&left>rightSum) return leftSum;
	if(rightSum>leftSum&&rightSum>midSum) return rightSum;
	return midSum;
}
public static int findMaxCro(int[] a,int left,int mid,int right){
	int maxleft,maxright;
	int sum=0;
	maxleft=a[mid];
	for(int i=mid;i>=left;i--){
		sum+=a[i];
		if(sum>maxleft){
			maxleft=sum;
		}
	}
	maxright=0;
	sum=0;
	for(int i=mid+1;i<=right;i++){
		sum+=a[i];
		if(sum>maxright){
			maxright=sum;
		}
	}
	return maxleft+maxright;
}

   //时间复杂度为O(n)
public static int getMaxSum3(int []a){
	int b=0;
	int sum=0;
	for(int i=0;i<a.length;i++){
		if(b>=0){
			b+=a[i];
		}else{
			b=a[i];
		}
		if(b>sum){
			sum=b;
		}
	}
	return sum;
}