最大子序列（java版)

 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;
     }
 }