leetcode 452. Minimum Number of Arrows to Burst Balloons

題目452. Minimum Number of Arrows to Burst Balloons
等級： medium
標籤：貪心

思路

對pair，以第一個元素爲第一排序準則，第二個元素爲次要準則排序。
然後從小到大掃描，尋找連續的有交疊部分的pair，然後銷燬，計數加一，繼續此操作至尾部，計數結果即爲答案

實現

# include <iostream>
# include <Vector>
# include <algorithm>

using namespace std;

bool cmp(pair<int, int> a, pair<int, int> b) {
    return a.first < b.first || (a.first == b.first && a.second < b.second);
}

class Solution {
public:
    int findMinArrowShots(vector<pair<int, int> >& points) {
        int size = points.size();
        if(size <= 1) return size;

        sort(points.begin(), points.end(), cmp);
        int index = 0, border = 0, ret = 0;
        border = points[index].second;

        while(1) {
            ret++;
            while(index < size && points[index].first <= border) {
                if(points[index].second < border)
                    border = points[index].second;
                index++;    
            };
            if(index >= size) break;

            // update the border
            border = points[index].second;  
        }   
        return ret;
    }
};