【LeetCode】贪心

[452] Minimum Number of Arrows to Burst Balloons[Medium]

给一堆线段，使用最少的arrow，穿过所有的线段。陈题，第一条线段的终点。

Input:
[[10,16], [2,8], [1,6], [7,12]]

Output:
2

Explanation:
One way is to shoot one arrow for example at x = 6 (bursting the balloons [2,8] and [1,6]) and another arrow at x = 11 (bursting the other two balloons).

 1 // 陈题。 第一条线段的终点。
 2 //wyzhang
 3 class Solution {
 4 public:
 5     static bool cmp(pair<int, int>& a, pair<int, int>& b) {
 6         return a.second < b.second;
 7     }
 8
 9     int findMinArrowShots(vector<pair<int, int>>& points) {
10         sort(points.begin(), points.end(), cmp);
11         vector<bool> valid_segments(points.size(), true);
12
13         int ans = 0;
14         for (size_t i = 0; i < points.size(); ++i) {
15             if(!valid_segments[i]) { // balloon has been shot
16                 continue;
17             }
18             const int end = points[i].second;
19             for (size_t j = i + 1; j < points.size(); ++j) {
20                 if (!valid_segments[j]) {
21                     continue;
22                 }
23                 if (end >= points[j].first) {
24                     valid_segments[j] = false;
25                 }
26             }
27             ans++;
28         }
29         return ans;
30     }
31 };