#include <iostream>
using namespace std;

//
// 题目：输入一个整形数组，数组里有正数也有负数。
// 数组中连续的一个或多个整数组成一个子数组，每个子数组都有一个和。
// 求所有子数组的和的最大值。要求时间复杂度为O(n)。
// 例如输入的数组为1, -2, 3, 10, -4, 7, 2, -5，和最大的子数组为3, 10, -4, 7, 2，
// 因此输出为该子数组的和18。
//

bool FindGreatestSumOfSubArray(int pData[], int nLength, int &nGreatestSum){
	// if the input is invalid, return false
	if (pData == NULL || nLength == 0)
		return false;
	
	int nCurSum = nGreatestSum = 0;

	for (int i = 0; i < nLength; i++){
		nCurSum += pData[i];
		// if the current sum is negative, discard it
		if (nCurSum < 0){
			nCurSum = 0;
		}
		// if a greater sum is found, update the greatest sum
		if (nCurSum > nGreatestSum){
			nGreatestSum = nCurSum;
		}
	}
	
	// if all data are negative, find the greatest element in the array
	if (nGreatestSum == 0){
		nGreatestSum = pData[0];
		for (int i = 1; i < nLength; i++){
			if (pData[i] > nGreatestSum){
				nGreatestSum = pData[i];
			}
		}
	}

	return true;
}


int _tmain(int argc, _TCHAR* argv[])
{
	int data[] = { 1, -2, 3, 10, -4, 7, 2, -5 };

	int nGreatestSum = 0;
	bool result = FindGreatestSumOfSubArray(data, sizeof(data) / sizeof(data[0]), nGreatestSum);
	if (result){
		cout << "nGreatestSum = " << nGreatestSum << endl;
	}
	else{
		cout << "Invalid input" << endl;
	}
	return 0;
}

测试结果:

nGreatestSum = 18