剑指Offer——（42）和为S的连续正数序列

//初始little数值为1，big数值为2
//当count等于sum时，添加序列
//否则判断
//当count大于sum时，后移little，big不动，使count减小，过程中count等于sum时，添加序列，直到little等于big
//当count小于sum时，后移big，使count增大
//直到little等于middle
//注意判断sum的值是否合法
class Solution
{
public:
vector<vector<int>> FindContinuousSequence(int sum)
{
vector<vector<int>> vec;
if (sum < 3)//防御性动作
return vec;
int little = 1;//左边界，即最小值
int big = 2;//右边界，即最大值
int middle = (sum + 1) / 2;//中间值
int count = little + big;//记录序列之和
while (little < middle)
{
if (count == sum)//当count等于sum使，添加序列
{
vector<int> tmp;
for (int i = little; i <= big; ++i)
tmp.push_back(i);
vec.push_back(tmp);
}
while (count > sum && little < middle)//此时count大于sum
{
count -= little;//减小count
++little;//后移最小值
if (count == sum)//count等于sum时，添加序列
{
vector<int> tmp;
for (int i = little; i <= big; ++i)
tmp.push_back(i);
vec.push_back(tmp);
}
}
++big;//此时，count小于sum，后移最大值，使count增大
count += big;
}
return vec;
}
};