|
| 1 | +--- |
| 2 | +comments: true |
| 3 | +difficulty: Medium |
| 4 | +edit_url: https://github.com/doocs/leetcode/edit/main/solution/0400-0499/0452.Minimum%20Number%20of%20Arrows%20to%20Burst%20Balloons/README_EN.md |
| 5 | +tags: |
| 6 | + - Greedy |
| 7 | + - Array |
| 8 | + - Sorting |
| 9 | +--- |
| 10 | + |
| 11 | +<!-- problem:start --> |
| 12 | + |
| 13 | +# [452. Minimum Number of Arrows to Burst Balloons](https://leetcode.com/problems/minimum-number-of-arrows-to-burst-balloons) |
| 14 | + |
| 15 | +[中文文档](/solution/0400-0499/0452.Minimum%20Number%20of%20Arrows%20to%20Burst%20Balloons/README.md) |
| 16 | + |
| 17 | +## Description |
| 18 | + |
| 19 | +<!-- description:start --> |
| 20 | + |
| 21 | +<p>There are some spherical balloons taped onto a flat wall that represents the XY-plane. The balloons are represented as a 2D integer array <code>points</code> where <code>points[i] = [x<sub>start</sub>, x<sub>end</sub>]</code> denotes a balloon whose <strong>horizontal diameter</strong> stretches between <code>x<sub>start</sub></code> and <code>x<sub>end</sub></code>. You do not know the exact y-coordinates of the balloons.</p> |
| 22 | + |
| 23 | +<p>Arrows can be shot up <strong>directly vertically</strong> (in the positive y-direction) from different points along the x-axis. A balloon with <code>x<sub>start</sub></code> and <code>x<sub>end</sub></code> is <strong>burst</strong> by an arrow shot at <code>x</code> if <code>x<sub>start</sub> <= x <= x<sub>end</sub></code>. There is <strong>no limit</strong> to the number of arrows that can be shot. A shot arrow keeps traveling up infinitely, bursting any balloons in its path.</p> |
| 24 | + |
| 25 | +<p>Given the array <code>points</code>, return <em>the <strong>minimum</strong> number of arrows that must be shot to burst all balloons</em>.</p> |
| 26 | + |
| 27 | +<p> </p> |
| 28 | +<p><strong class="example">Example 1:</strong></p> |
| 29 | + |
| 30 | +<pre> |
| 31 | +<strong>Input:</strong> points = [[10,16],[2,8],[1,6],[7,12]] |
| 32 | +<strong>Output:</strong> 2 |
| 33 | +<strong>Explanation:</strong> The balloons can be burst by 2 arrows: |
| 34 | +- Shoot an arrow at x = 6, bursting the balloons [2,8] and [1,6]. |
| 35 | +- Shoot an arrow at x = 11, bursting the balloons [10,16] and [7,12]. |
| 36 | +</pre> |
| 37 | + |
| 38 | +<p><strong class="example">Example 2:</strong></p> |
| 39 | + |
| 40 | +<pre> |
| 41 | +<strong>Input:</strong> points = [[1,2],[3,4],[5,6],[7,8]] |
| 42 | +<strong>Output:</strong> 4 |
| 43 | +<strong>Explanation:</strong> One arrow needs to be shot for each balloon for a total of 4 arrows. |
| 44 | +</pre> |
| 45 | + |
| 46 | +<p><strong class="example">Example 3:</strong></p> |
| 47 | + |
| 48 | +<pre> |
| 49 | +<strong>Input:</strong> points = [[1,2],[2,3],[3,4],[4,5]] |
| 50 | +<strong>Output:</strong> 2 |
| 51 | +<strong>Explanation:</strong> The balloons can be burst by 2 arrows: |
| 52 | +- Shoot an arrow at x = 2, bursting the balloons [1,2] and [2,3]. |
| 53 | +- Shoot an arrow at x = 4, bursting the balloons [3,4] and [4,5]. |
| 54 | +</pre> |
| 55 | + |
| 56 | +<p> </p> |
| 57 | +<p><strong>Constraints:</strong></p> |
| 58 | + |
| 59 | +<ul> |
| 60 | + <li><code>1 <= points.length <= 10<sup>5</sup></code></li> |
| 61 | + <li><code>points[i].length == 2</code></li> |
| 62 | + <li><code>-2<sup>31</sup> <= x<sub>start</sub> < x<sub>end</sub> <= 2<sup>31</sup> - 1</code></li> |
| 63 | +</ul> |
| 64 | + |
| 65 | +<!-- description:end --> |
| 66 | + |
| 67 | +## Solutions |
| 68 | + |
| 69 | +<!-- solution:start --> |
| 70 | + |
| 71 | +### Solution 1 |
| 72 | + |
| 73 | +<!-- tabs:start --> |
| 74 | + |
| 75 | +#### Python3 |
| 76 | + |
| 77 | +```python |
| 78 | +class Solution: |
| 79 | + def findMinArrowShots(self, points: List[List[int]]) -> int: |
| 80 | + ans, last = 0, -inf |
| 81 | + for a, b in sorted(points, key=lambda x: x[1]): |
| 82 | + if a > last: |
| 83 | + ans += 1 |
| 84 | + last = b |
| 85 | + return ans |
| 86 | +``` |
| 87 | + |
| 88 | +#### Java |
| 89 | + |
| 90 | +```java |
| 91 | +class Solution { |
| 92 | + public int findMinArrowShots(int[][] points) { |
| 93 | + // 直接 a[1] - b[1] 可能会溢出 |
| 94 | + Arrays.sort(points, Comparator.comparingInt(a -> a[1])); |
| 95 | + int ans = 0; |
| 96 | + long last = -(1L << 60); |
| 97 | + for (var p : points) { |
| 98 | + int a = p[0], b = p[1]; |
| 99 | + if (a > last) { |
| 100 | + ++ans; |
| 101 | + last = b; |
| 102 | + } |
| 103 | + } |
| 104 | + return ans; |
| 105 | + } |
| 106 | +} |
| 107 | +``` |
| 108 | + |
| 109 | +#### C++ |
| 110 | + |
| 111 | +```cpp |
| 112 | +class Solution { |
| 113 | +public: |
| 114 | + int findMinArrowShots(vector<vector<int>>& points) { |
| 115 | + sort(points.begin(), points.end(), [](vector<int>& a, vector<int>& b) { |
| 116 | + return a[1] < b[1]; |
| 117 | + }); |
| 118 | + int ans = 0; |
| 119 | + long long last = -(1LL << 60); |
| 120 | + for (auto& p : points) { |
| 121 | + int a = p[0], b = p[1]; |
| 122 | + if (a > last) { |
| 123 | + ++ans; |
| 124 | + last = b; |
| 125 | + } |
| 126 | + } |
| 127 | + return ans; |
| 128 | + } |
| 129 | +}; |
| 130 | +``` |
| 131 | +
|
| 132 | +#### Go |
| 133 | +
|
| 134 | +```go |
| 135 | +func findMinArrowShots(points [][]int) (ans int) { |
| 136 | + sort.Slice(points, func(i, j int) bool { return points[i][1] < points[j][1] }) |
| 137 | + last := -(1 << 60) |
| 138 | + for _, p := range points { |
| 139 | + a, b := p[0], p[1] |
| 140 | + if a > last { |
| 141 | + ans++ |
| 142 | + last = b |
| 143 | + } |
| 144 | + } |
| 145 | + return |
| 146 | +} |
| 147 | +``` |
| 148 | + |
| 149 | +#### TypeScript |
| 150 | + |
| 151 | +```ts |
| 152 | +function findMinArrowShots(points: number[][]): number { |
| 153 | + points.sort((a, b) => a[1] - b[1]); |
| 154 | + let ans = 0; |
| 155 | + let last = -Infinity; |
| 156 | + for (const [a, b] of points) { |
| 157 | + if (last < a) { |
| 158 | + ans++; |
| 159 | + last = b; |
| 160 | + } |
| 161 | + } |
| 162 | + return ans; |
| 163 | +} |
| 164 | +``` |
| 165 | + |
| 166 | +#### C# |
| 167 | + |
| 168 | +```cs |
| 169 | +public class Solution { |
| 170 | + public int FindMinArrowShots(int[][] points) { |
| 171 | + Array.Sort(points, (a, b) => a[1] < b[1] ? -1 : a[1] > b[1] ? 1 : 0); |
| 172 | + int ans = 0; |
| 173 | + long last = long.MinValue; |
| 174 | + foreach (var point in points) { |
| 175 | + if (point[0] > last) { |
| 176 | + ++ans; |
| 177 | + last = point[1]; |
| 178 | + } |
| 179 | + } |
| 180 | + return ans; |
| 181 | + } |
| 182 | +} |
| 183 | +``` |
| 184 | + |
| 185 | +<!-- tabs:end --> |
| 186 | + |
| 187 | +<!-- solution:end --> |
| 188 | + |
| 189 | +<!-- problem:end --> |
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