452

Author: tech-cow

README.md

@@ -102,6 +102,10 @@ Success is like pregnancy, Everybody congratulates you but nobody knows how many
 |40|[Combination Sum II](https://leetcode.com/problems/combination-sum-ii/#/solutions)| [Python [Yu]](./backtrack/Yu/39.py) | _O(K * (2^N)_| _O(N)_  | Medium | |[公瑾讲解](https://youtu.be/HdS5dOaz-mk)|
 |216|[Combination Sum III](https://leetcode.com/problems/combination-sum-iii/#/description)| [Python [Yu]](./backtrack/Yu/216.py) | _O(K * (2^N)_| _O(N)_  | Medium | ||
 
+## Greedy Medium
+|  #  | Title | Solution | Time | Space | Difficulty | Note|
+|-----|-------| -------- | ---- | ------|------------|-----|
+|452|[Minimum Number of Arrows to Burst Balloons](https://leetcode.com/problems/minimum-number-of-arrows-to-burst-balloons/#/description)| [Python [Yu]](./greedy/452.py) | _O(N)_| _O(1)_  | Medium| |
 
 ## Dynamic Programming Easy
 |  #  | Title | Solution | Time | Space | Difficulty | Note|

greedy/452.py

@@ -0,0 +1,26 @@
+#!/usr/bin/python
+# -*- coding: utf-8 -*-
+
+# Author: Yu Zhou
+# 452. Minimum Number of Arrows to Burst Balloons
+
+# 用到了Greedy的一个，扫描线的运用
+# 先进行排序，然后在每次循环的时候
+# 比对end point，然后更新end point，若超出end point范围，则增加一个arrow
+# 这道题的知识点是扫描线+ 如何sort 一个tuple里面的第一个值
+
+class Solution(object):
+    def findMinArrowShots(self, points):
+        """
+        :type points: List[List[int]]
+        :rtype: int
+        """
+
+        points = sorted(points, key = lambda x: x[1])
+        end = -float('inf')
+        res = 0
+        for ballon in points:
+            if ballon[0] > end:
+                end = ballon[1]
+                res += 1
+        return res