#2731
Movement of Robots
expert · 1145 · lc medium +32 · verified · 27.9% accepted · 542 likes · top 6%
Description
Robots start at positions given by nums on an infinite number line, each moving in the direction from string s ('L' or 'R') at one unit per second. Colliding robots reverse directions. After d seconds, return the sum of pairwise distances between all robots, modulo 109 + 7.
Example 1:
Input: nums = [-2,0,2], s = "RLL", d = 3
Output: 8
Explanation:
After 1 second, the positions are [-1,-1,1]. Now, the robot at index 0 will move left, and the robot at index 1 will move right.
After 2 seconds, the positions are [-2,0,0]. Now, the robot at index 1 will move left, and the robot at index 2 will move right.
After 3 seconds, the positions are [-3,-1,1].
The distance between the robot at index 0 and 1 is abs(-3 - (-1)) = 2.
The distance between the robot at index 0 and 2 is abs(-3 - 1) = 4.
The distance between the robot at index 1 and 2 is abs(-1 - 1) = 2.
The sum of the pairs of all distances = 2 + 4 + 2 = 8.
Example 2:
Input: nums = [1,0], s = "RL", d = 2
Output: 5
Explanation:
After 1 second, the positions are [2,-1].
After 2 seconds, the positions are [3,-2].
The distance between the two robots is abs(-2 - 3) = 5.
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