mirror of
https://gitee.com/coder-xiaomo/leetcode-problemset
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169 lines
17 KiB
JSON
169 lines
17 KiB
JSON
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"questionId": "2317",
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"title": "Count Collisions on a Road",
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"titleSlug": "count-collisions-on-a-road",
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"content": "<p>There are <code>n</code> cars on an infinitely long road. The cars are numbered from <code>0</code> to <code>n - 1</code> from left to right and each car is present at a <strong>unique</strong> point.</p>\n\n<p>You are given a <strong>0-indexed</strong> string <code>directions</code> of length <code>n</code>. <code>directions[i]</code> can be either <code>'L'</code>, <code>'R'</code>, or <code>'S'</code> denoting whether the <code>i<sup>th</sup></code> car is moving towards the <strong>left</strong>, towards the <strong>right</strong>, or <strong>staying</strong> at its current point respectively. Each moving car has the <strong>same speed</strong>.</p>\n\n<p>The number of collisions can be calculated as follows:</p>\n\n<ul>\n\t<li>When two cars moving in <strong>opposite</strong> directions collide with each other, the number of collisions increases by <code>2</code>.</li>\n\t<li>When a moving car collides with a stationary car, the number of collisions increases by <code>1</code>.</li>\n</ul>\n\n<p>After a collision, the cars involved can no longer move and will stay at the point where they collided. Other than that, cars cannot change their state or direction of motion.</p>\n\n<p>Return <em>the <strong>total number of collisions</strong> that will happen on the road</em>.</p>\n\n<p> </p>\n<p><strong>Example 1:</strong></p>\n\n<pre>\n<strong>Input:</strong> directions = "RLRSLL"\n<strong>Output:</strong> 5\n<strong>Explanation:</strong>\nThe collisions that will happen on the road are:\n- Cars 0 and 1 will collide with each other. Since they are moving in opposite directions, the number of collisions becomes 0 + 2 = 2.\n- Cars 2 and 3 will collide with each other. Since car 3 is stationary, the number of collisions becomes 2 + 1 = 3.\n- Cars 3 and 4 will collide with each other. Since car 3 is stationary, the number of collisions becomes 3 + 1 = 4.\n- Cars 4 and 5 will collide with each other. After car 4 collides with car 3, it will stay at the point of collision and get hit by car 5. The number of collisions becomes 4 + 1 = 5.\nThus, the total number of collisions that will happen on the road is 5. \n</pre>\n\n<p><strong>Example 2:</strong></p>\n\n<pre>\n<strong>Input:</strong> directions = "LLRR"\n<strong>Output:</strong> 0\n<strong>Explanation:</strong>\nNo cars will collide with each other. Thus, the total number of collisions that will happen on the road is 0.</pre>\n\n<p> </p>\n<p><strong>Constraints:</strong></p>\n\n<ul>\n\t<li><code>1 <= directions.length <= 10<sup>5</sup></code></li>\n\t<li><code>directions[i]</code> is either <code>'L'</code>, <code>'R'</code>, or <code>'S'</code>.</li>\n</ul>\n",
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"difficulty": "Medium",
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"exampleTestcases": "\"RLRSLL\"\n\"LLRR\"",
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"categoryTitle": "Algorithms",
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"code": "class Solution {\npublic:\n int countCollisions(string directions) {\n \n }\n};",
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"code": "-spec count_collisions(Directions :: unicode:unicode_binary()) -> integer().\ncount_collisions(Directions) ->\n .",
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"code": "defmodule Solution do\n @spec count_collisions(directions :: String.t) :: integer\n def count_collisions(directions) do\n\n end\nend",
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"hints": [
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"In what circumstances does a moving car not collide with another car?",
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"If we disregard the moving cars that do not collide with another car, what does each moving car contribute to the answer?",
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"Will stationary cars contribute towards the answer?"
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],
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"sampleTestCase": "\"RLRSLL\"",
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