Get a random number focused on center

Question

Is it possible to get a random number between 1-100 and keep the results mainly within the 40-60 range? I mean, it will go out of that range rarely, but I want it to be main

Answer 1

This answer is really good. But I would like to post implementation instructions (I'm not into JavaScript, so I hope you will understand) for different situation.

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Assume you have ranges and weights for every range:

ranges - [1, 20], [21, 40], [41, 60], [61, 100]
weights - {1, 2, 100, 5}

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Initial Static Information, could be cached:

1. Sum of all weights (108 in sample)
2. Range selection boundaries. It basically this formula: Boundary[n] = Boundary[n - 1] + weigh[n - 1] and Boundary[0] = 0. Sample has Boundary = {0, 1, 3, 103, 108}

Number generation:

1. Generate random number N from range [0, Sum of all weights).
2. for (i = 0; i < size(Boundary) && N > Boundary[i + 1]; ++i)
3. Take ith range and generate random number in that range.

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Additional note for performance optimizations. Ranges don't have to be ordered neither ascending nor descending order, so for faster range look-up range that has highest weight should go first and one with lowest weight should go last.