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46 lines
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46 lines
2.7 KiB
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<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>
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<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>
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<p>The number of collisions can be calculated as follows:</p>
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<ul>
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<li>When two cars moving in <strong>opposite</strong> directions collide with each other, the number of collisions increases by <code>2</code>.</li>
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<li>When a moving car collides with a stationary car, the number of collisions increases by <code>1</code>.</li>
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</ul>
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<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>
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<p>Return <em>the <strong>total number of collisions</strong> that will happen on the road</em>.</p>
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<p> </p>
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<p><strong class="example">Example 1:</strong></p>
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<pre>
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<strong>Input:</strong> directions = "RLRSLL"
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<strong>Output:</strong> 5
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<strong>Explanation:</strong>
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The collisions that will happen on the road are:
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- Cars 0 and 1 will collide with each other. Since they are moving in opposite directions, the number of collisions becomes 0 + 2 = 2.
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- Cars 2 and 3 will collide with each other. Since car 3 is stationary, the number of collisions becomes 2 + 1 = 3.
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- Cars 3 and 4 will collide with each other. Since car 3 is stationary, the number of collisions becomes 3 + 1 = 4.
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- 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.
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Thus, the total number of collisions that will happen on the road is 5.
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</pre>
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<p><strong class="example">Example 2:</strong></p>
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<pre>
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<strong>Input:</strong> directions = "LLRR"
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<strong>Output:</strong> 0
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<strong>Explanation:</strong>
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No cars will collide with each other. Thus, the total number of collisions that will happen on the road is 0.</pre>
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<p> </p>
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<p><strong>Constraints:</strong></p>
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<ul>
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<li><code>1 <= directions.length <= 10<sup>5</sup></code></li>
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<li><code>directions[i]</code> is either <code>'L'</code>, <code>'R'</code>, or <code>'S'</code>.</li>
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</ul>
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