Java--最大子序列和实现

Posted 2020-08-20 小董斌

 

package com.dongbin.test;

/**
 * 最大子序列和 --分治法
 * 
 * @author dongbin
 *
 */
public class MaxSubListSum {

    /**
     * 最大子序列的实现方法
     * 
     * @param arr
     *            --数组
     * @param left
     * @param right
     * @return
     */
    public static int maxsubListSum(int arr[], int left, int right) {

        if (left == right) {// arr.length==1
            if (arr[left] > 0) {
                return arr[left];
            } else {
                return 0;
            }
        }

        // 划分数组
        int center = (left + right) / 2;
        int maxLeftSum = maxsubListSum(arr, left, center);// 左边最大值
        int maxRightSum = maxsubListSum(arr, center + 1, right);// 右边最大值

        // 左边求和
        int maxLeftBorderSum = 0, leftBorderSum = 0;
        for (int i = center; i >= left; i--) {
            leftBorderSum += arr[i];
            if (leftBorderSum > maxLeftBorderSum) {
                maxLeftBorderSum = leftBorderSum;
            }
        }

        // 右边求和
        int maxRightBorderSum = 0, rightBorderSum = 0;
        for(int i = center+1;i<=right;i++){
            rightBorderSum += arr[i];
            if(rightBorderSum>maxRightBorderSum){
                maxRightBorderSum = rightBorderSum;
            }            
        }
        
        return maxList(maxLeftSum,maxRightSum,maxLeftBorderSum+maxRightBorderSum);
        
    }
    
    /**
     * 获取 多个Id 的最大值
     * @param elements
     * @return
     */
    private static  int maxList(int... elements){
        int max = 0;
        for(int i = 0;i<elements.length;i++){
            if(elements[i]>max){
                max = elements[i];
            }
        }
        return max;
    }
    
    public static void main(String[] args) {
        int[] a = {4,-3,5,-2,-1,2,6,-2};
        System.out.println(maxsubListSum(a, 0, a.length-1));
    }
}

 

/**
     * 优化最大子序列
     * @param arr
     * @return
     */
    public static int optMaxSubListSum(int [] arr){
        int maxSum = 0,temp = 0;
        for(int i=0;i<arr.length;i++){
            temp += arr[i];
            if(temp>maxSum){
                maxSum = temp;
            }
            
            if(temp<0){
                temp = 0;
            }
        }
        
        return maxSum;
    }