|
| 1 | +## 1. Stack |
| 2 | + |
| 3 | +::tabs-start |
| 4 | + |
| 5 | +```python |
| 6 | +class Solution: |
| 7 | + def asteroidCollision(self, asteroids: List[int]) -> List[int]: |
| 8 | + stack = [] |
| 9 | + for a in asteroids: |
| 10 | + while stack and a < 0 and stack[-1] > 0: |
| 11 | + diff = a + stack[-1] |
| 12 | + if diff < 0: |
| 13 | + stack.pop() |
| 14 | + elif diff > 0: |
| 15 | + a = 0 |
| 16 | + else: |
| 17 | + a = 0 |
| 18 | + stack.pop() |
| 19 | + if a: |
| 20 | + stack.append(a) |
| 21 | + return stack |
| 22 | +``` |
| 23 | + |
| 24 | +```java |
| 25 | +public class Solution { |
| 26 | + public int[] asteroidCollision(int[] asteroids) { |
| 27 | + Stack<Integer> stack = new Stack<>(); |
| 28 | + for (int a : asteroids) { |
| 29 | + while (!stack.isEmpty() && a < 0 && stack.peek() > 0) { |
| 30 | + int diff = a + stack.peek(); |
| 31 | + if (diff < 0) { |
| 32 | + stack.pop(); |
| 33 | + } else if (diff > 0) { |
| 34 | + a = 0; |
| 35 | + } else { |
| 36 | + a = 0; |
| 37 | + stack.pop(); |
| 38 | + } |
| 39 | + } |
| 40 | + if (a != 0) { |
| 41 | + stack.add(a); |
| 42 | + } |
| 43 | + } |
| 44 | + return stack.stream().mapToInt(i -> i).toArray(); |
| 45 | + } |
| 46 | +} |
| 47 | +``` |
| 48 | + |
| 49 | +```cpp |
| 50 | +class Solution { |
| 51 | +public: |
| 52 | + vector<int> asteroidCollision(vector<int>& asteroids) { |
| 53 | + vector<int> stack; |
| 54 | + for (int& a : asteroids) { |
| 55 | + while (!stack.empty() && a < 0 && stack.back() > 0) { |
| 56 | + int diff = a + stack.back(); |
| 57 | + if (diff < 0) { |
| 58 | + stack.pop_back(); |
| 59 | + } else if (diff > 0) { |
| 60 | + a = 0; |
| 61 | + } else { |
| 62 | + a = 0; |
| 63 | + stack.pop_back(); |
| 64 | + } |
| 65 | + } |
| 66 | + if (a != 0) { |
| 67 | + stack.push_back(a); |
| 68 | + } |
| 69 | + } |
| 70 | + return stack; |
| 71 | + } |
| 72 | +}; |
| 73 | +``` |
| 74 | +
|
| 75 | +```javascript |
| 76 | +class Solution { |
| 77 | + /** |
| 78 | + * @param {number[]} asteroids |
| 79 | + * @return {number[]} |
| 80 | + */ |
| 81 | + asteroidCollision(asteroids) { |
| 82 | + const stack = []; |
| 83 | + for (let a of asteroids) { |
| 84 | + while (stack.length && a < 0 && stack[stack.length - 1] > 0) { |
| 85 | + const diff = a + stack[stack.length - 1]; |
| 86 | + if (diff < 0) { |
| 87 | + stack.pop(); |
| 88 | + } else if (diff > 0) { |
| 89 | + a = 0; |
| 90 | + } else { |
| 91 | + a = 0; |
| 92 | + stack.pop(); |
| 93 | + } |
| 94 | + } |
| 95 | + if (a !== 0) { |
| 96 | + stack.push(a); |
| 97 | + } |
| 98 | + } |
| 99 | + return stack; |
| 100 | + } |
| 101 | +} |
| 102 | +``` |
| 103 | + |
| 104 | +::tabs-end |
| 105 | + |
| 106 | +### Time & Space Complexity |
| 107 | + |
| 108 | +* Time complexity: $O(n)$ |
| 109 | +* Space complexity: $O(n)$ |
| 110 | + |
| 111 | +--- |
| 112 | + |
| 113 | +## 2. Without Stack |
| 114 | + |
| 115 | +::tabs-start |
| 116 | + |
| 117 | +```python |
| 118 | +class Solution: |
| 119 | + def asteroidCollision(self, asteroids: List[int]) -> List[int]: |
| 120 | + n = len(asteroids) |
| 121 | + j = -1 |
| 122 | + |
| 123 | + for a in asteroids: |
| 124 | + while j >= 0 and asteroids[j] > 0 and a < 0: |
| 125 | + if asteroids[j] > abs(a): |
| 126 | + a = 0 |
| 127 | + break |
| 128 | + elif asteroids[j] == abs(a): |
| 129 | + j -= 1 |
| 130 | + a = 0 |
| 131 | + break |
| 132 | + else: |
| 133 | + j -= 1 |
| 134 | + if a: |
| 135 | + j += 1 |
| 136 | + asteroids[j] = a |
| 137 | + |
| 138 | + return asteroids[:j + 1] |
| 139 | +``` |
| 140 | + |
| 141 | +```java |
| 142 | +public class Solution { |
| 143 | + public int[] asteroidCollision(int[] asteroids) { |
| 144 | + int n = asteroids.length; |
| 145 | + int j = -1; |
| 146 | + |
| 147 | + for (int a : asteroids) { |
| 148 | + while (j >= 0 && asteroids[j] > 0 && a < 0) { |
| 149 | + if (asteroids[j] > Math.abs(a)) { |
| 150 | + a = 0; |
| 151 | + break; |
| 152 | + } else if (asteroids[j] == Math.abs(a)) { |
| 153 | + j--; |
| 154 | + a = 0; |
| 155 | + break; |
| 156 | + } else { |
| 157 | + j--; |
| 158 | + } |
| 159 | + } |
| 160 | + if (a != 0) { |
| 161 | + asteroids[++j] = a; |
| 162 | + } |
| 163 | + } |
| 164 | + |
| 165 | + return Arrays.copyOfRange(asteroids, 0, j + 1); |
| 166 | + } |
| 167 | +} |
| 168 | +``` |
| 169 | + |
| 170 | +```cpp |
| 171 | +class Solution { |
| 172 | +public: |
| 173 | + vector<int> asteroidCollision(vector<int>& asteroids) { |
| 174 | + int n = asteroids.size(); |
| 175 | + int j = -1; |
| 176 | + |
| 177 | + for (int& a : asteroids) { |
| 178 | + while (j >= 0 && asteroids[j] > 0 && a < 0) { |
| 179 | + if (asteroids[j] > abs(a)) { |
| 180 | + a = 0; |
| 181 | + break; |
| 182 | + } else if (asteroids[j] == abs(a)) { |
| 183 | + j--; |
| 184 | + a = 0; |
| 185 | + break; |
| 186 | + } else { |
| 187 | + j--; |
| 188 | + } |
| 189 | + } |
| 190 | + if (a != 0) { |
| 191 | + asteroids[++j] = a; |
| 192 | + } |
| 193 | + } |
| 194 | + |
| 195 | + asteroids.resize(j + 1); |
| 196 | + return asteroids; |
| 197 | + } |
| 198 | +}; |
| 199 | +``` |
| 200 | + |
| 201 | +```javascript |
| 202 | +class Solution { |
| 203 | + /** |
| 204 | + * @param {number[]} asteroids |
| 205 | + * @return {number[]} |
| 206 | + */ |
| 207 | + asteroidCollision(asteroids) { |
| 208 | + let n = asteroids.length; |
| 209 | + let j = -1; |
| 210 | + |
| 211 | + for (let a of asteroids) { |
| 212 | + while (j >= 0 && asteroids[j] > 0 && a < 0) { |
| 213 | + if (asteroids[j] > Math.abs(a)) { |
| 214 | + a = 0; |
| 215 | + break; |
| 216 | + } else if (asteroids[j] === Math.abs(a)) { |
| 217 | + j--; |
| 218 | + a = 0; |
| 219 | + break; |
| 220 | + } else { |
| 221 | + j--; |
| 222 | + } |
| 223 | + } |
| 224 | + if (a !== 0) { |
| 225 | + asteroids[++j] = a; |
| 226 | + } |
| 227 | + } |
| 228 | + |
| 229 | + return asteroids.slice(0, j + 1); |
| 230 | + } |
| 231 | +} |
| 232 | +``` |
| 233 | + |
| 234 | +::tabs-end |
| 235 | + |
| 236 | +### Time & Space Complexity |
| 237 | + |
| 238 | +* Time complexity: $O(n)$ |
| 239 | +* Space complexity: $O(n)$ for the output array. |
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