package com.algorithm.test;

 /**

  * 最大子序列

  * @author LiFen

  *

  */

 public class LargestSubsequence {

     public static void main(String[] args) {

         int[] arr = {,-,,-,-,,,-};

         System.out.println(maxSubSum(arr));

         System.out.println(maxSumRec(arr, , arr.length - ));

         System.out.println(maxSubSum2(arr));

     }

     /*

      * 时间复杂度O(N*N)

      */

     public static int maxSubSum(int [] a) {

         int maxSum = ;

         for(int i = ; i < a.length; i++) {

             int thisSum = ;

             for(int j = ; j < a.length; j++) {

                 thisSum += a[j];

                 if(thisSum > maxSum)

                     maxSum = thisSum;

             }

         }

         return maxSum;

     }

     /*

      * 递归

      * 时间复杂度O(N logN)

      */

     public static int maxSumRec(int [] a, int left, int right) {

         if(left == right) {

             if(a[left] > )

                 return a[left];

             else return ;

         }

         int center = (left + right) / ;

         int maxLeftSum = maxSumRec(a, left, center);

         int maxRightSum = maxSumRec(a, center + , right);

         int maxLeftBorderSum = ,leftBorderSum = ;

         for(int i = center; i >= left; i--) {

             leftBorderSum += a[i];

             if(leftBorderSum > maxLeftBorderSum)

                 maxLeftBorderSum = leftBorderSum;

         }

         int maxRightBorderSum = , rightBoderSum = ;

         for(int i = center + ; i <= right; i++) {

             rightBoderSum += a[i];

             if(rightBoderSum > maxRightBorderSum)

                 maxRightBorderSum = rightBoderSum;

         }

         return Math.max(Math.max(maxLeftSum, maxRightSum),maxLeftBorderSum + maxRightBorderSum);

     }

     /*

      * 联机算法

      * 快

      */

     public static int maxSubSum2(int [] a) {

         int maxSum = , thisSum = ;

         for(int i = ; i < a.length; i++) {

             thisSum += a[i];

             if(thisSum > maxSum) {

                 maxSum = thisSum;

             }else if(thisSum < ){

                 thisSum = ;

             }

         }

         return maxSum;

     }

 }