406. Queue Reconstruction by Height

Description

height of the person and k is the number of people in front of this person who have a height greater than or equal to h. Write an algorithm to reconstruct the queue.

Note:
The number of people is less than 1,100.

Example

Input:
[[7,0], [4,4], [7,1], [5,0], [6,1], [5,2]]

Output:
[[5,0], [7,0], [5,2], [6,1], [4,4], [7,1]]

簡要題解：

這道題總的解題方向是採用貪心算法。具體做法是不斷循壞people向量的各個元素直到該向量爲空。每次從people中取出一個，在result中找到一個剛好可以放的位置放入。如果找不到可以放的位置放就跳過這個元素，等待下一輪循壞再繼續找位置。

但是這樣做會有點問題，我們必須保證後放入result的元素不會影響到先放入result的元素。因此，需要對people中的每個人按身高大小由高到底排序。（身高較低的不管怎麼放都不會影響到身高較高的人）。還要注意到，對於兩個身高相同的情況，k值小的應該放在前面。因爲，身高相同的兩個人，在result中k值小的一定是放在k值較大的那個人的前面。也就是說，在身高相同的情況下，k值較小的可能會影響k值較大的那個人。排完序後，就採用前面說的那種貪心算法來構造result就可得到正確的結果。

代碼：

class Solution {
public:
    static vector<pair<int, int> > reconstructQueue(vector<pair<int, int> >& people) {
        vector<pair<int, int> > result;

        for (int i = 0; i < people.size(); i++)
            for (int j = i + 1; j < people.size(); j++)
                if ((people[i].first < people[j].first) ||
                    (people[i].first == people[j].first && people[i].second > people[j].second)) {
                    pair<int, int> temp = people[i];
                    people[i] = people[j];
                    people[j] = temp;
                }

        while (!people.empty()) {
            vector<pair<int, int> >::iterator iter1, iter2;
            for (iter1 = people.begin(); iter1 != people.end(); iter1++) {
                int count = 0;
                int flag = false;
                for (iter2 = result.begin(); iter2 != result.end(); iter2++) {
                    if (count == iter1->second + 1) {
                        iter2--;
                        result.insert(iter2, *iter1);
                        people.erase(iter1);
                        flag = true;
                        break;
                    }
                    if (iter2->first >= iter1->first)
                        count++;
                }

                if (!flag && count == iter1->second + 1) {
                    pair<int, int> temp = result[result.size()-1];
                    result[result.size()-1] = *iter1;
                    result.push_back(temp);
                    people.erase(iter1);
                    flag = true;
                }

                if (!flag && count == iter1->second) {
                    result.push_back(*iter1);
                    people.erase(iter1);
                    flag = true;
                }

                if (flag)
                    break;
            }
        }

        return result;
    }
};