求数组中最大子序列和的问题

Posted 2022-04-22 menghejiuqian

/**
 * 创建人：yang.liu
 * 创建时间：2019/7/17 17:53
 * 版本：1.0
 * 内容描述：求最大子序列问题
 */
public class MaxSubSequenceSample 

    public static void main(String[] args) 
        var arr = new int[]-1, 2, 3, 4, 5, 6, 7, 8, 9, 10, -9, 20, -6, 5;
        int i = maxSubSequence(arr);
        System.out.println(i);

        int i1 = maxSubSequence2(arr);
        System.out.println(i1);
    

    /**
     * 时间复杂度为O(n^2)
     */
    public static int maxSubSequence(int[] arr) 

        int maxSum = 0;

        for (int i = 0; i < arr.length; i++) 
            int iSum = 0;
            for (int j = i; j < arr.length; j++) 
                iSum += arr[j];
                if (iSum > maxSum) 
                    maxSum = iSum;
                
            
        
        return maxSum;
    

    /**
     * Kadane算法
     * 时间复杂度为O(n^2)
     * 视频讲解：https://www.bilibili.com/video/av52421507?from=search&seid=3623534585276596200
     *          https://www.youtube.com/watch?v=86CQq3pKSUw
     */
    public static int maxSubSequence2(int[] arr) 

        int maxSum = arr[0];
        int iSum = 0;

        for (int i = 0; i < arr.length; i++) 
            iSum = Math.max(arr[i], iSum + arr[i]);
            if (iSum < 0) 
                iSum = 0;
            
            if (iSum > maxSum) 
                maxSum = iSum;
            
        
        return maxSum;
    


/**
 * 欢迎评论、留言、发表看法。谢谢！
 */