[编程题]和为S的连续正数序列

class Solution {
public:
    vector<vector<int> > FindContinuousSequence(int sum) {
        vector<vector<int>> res;
        if(sum < 3)
            return res;
        // 边界值
        int small = 1;
        int big = 2;
        // 初试累加
        int calculate = small + big;
        // 限定边界为 sum 的一半
        while(small < (sum + 1) /2 ){
            // 相等，保存结果，前进big
            if(calculate == sum){
                vector<int> line;
                for(int i = small; i <= big; ++i)
                    line.push_back(i);
                res.push_back(line);
                calculate += ++big;
            }
            // 过小，加数，前进big
            else if(calculate < sum)
                calculate += ++big;
            // 过大，减数，前进small
            else
                calculate -= small++;
        }
        return res;
    }
};