HDOJ1003.Max Sum

试题请参见: http://acm.hdu.edu.cn/showproblem.php?pid=1003

题目概述

Given a sequence a[1],a[2],a[3]……a
, your job is to calculate the max sum of a sub-sequence. For example, given (6,-1,5,4,-7), the max sum in this sequence is 6 + (-1) + 5 + 4 = 14.

解题思路

最大子序列问题. 存在O(n)的解法.

遇到的问题

对于子序列

(-100, -10, -1000)

始终无法获得正确结果.

源代码

#include <iostream>

const int MAX_SIZE = 100000;
int arr[MAX_SIZE];

int main() {
int t = 0;
std::cin >> t;

for ( int i = 1; i <= t; ++ i ) {
int n = 0;
std::cin >> n;
for ( int j = 0; j < n; ++ j ) {
std::cin >> arr[j];
}

int startIndex = 0, currentStartIndex = 0, endIndex = 0;
int maxSum = -2147483648, currentSum = 0;
for ( int j = 0; j < n; ++ j ) {
currentSum += arr[j];

if ( currentSum > maxSum ) {
startIndex = currentStartIndex;
endIndex = j;
maxSum = currentSum;

}
if ( currentSum < 0 ) {
currentStartIndex = j + 1;
currentSum = 0;
}
}

std::cout << "Case " << i << ":" << std::endl;
std::cout << maxSum << " " << startIndex + 1 << " " << endIndex + 1 << std::endl;

if ( i != t ) {
std::cout << std::endl;
}
}
return 0;
}