generate sequences of numbers with variable degree of randomness

variable_randomness.cpp

#if 0
g++ -std=c++11 -Wall -Wextra -pedantic -Werror $0 || exit 1
exec ./a.out
#endif

// generate sequences of numbers 0..(1-n) with variable degree of randomness:
// r = 0.0 -> perfectly sorted
// r = 0.5 -> fully shuffled
// r = 1.0 -> perfectly reversed

#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <vector>
#include <algorithm>

inline float lerp(float a, float b, float t) {
    return a + (b - a) * t;
}

std::vector<int> generateVariableRandomness(int n, float r) {
    struct key {
        float w;
        int i;
        inline bool operator<(const key& other) { return w < other.w; }
    };
    std::vector<key> keys(n);
    float reverse = (r > 0.5f) ? 1.0f : 0.0f;
    r = 1.0f - 2.0f * fabsf(r - 0.5f);
    for (int i = 0;  i < n;  ++i) {
        keys[i].i = i;
        keys[i].w = lerp(fabsf(reverse - i / (float)(n - 1)), rand() / (float)RAND_MAX, r);
    }
    std::sort(keys.begin(), keys.end());
    std::vector<int> result(n);
    for (int i = 0;  i < n;  ++i) {
        result[i] = keys[i].i;
    }
    return result;
}


int main() {
    srand(0x47110815);
    for (float r = 0.0f;  r <= 1.0f;  r += 1.0f / 16) {
        printf("%5.3f: ", r);
        std::vector<int> seq = generateVariableRandomness(26, r);
        for (int i = 0;  i < 26;  ++i) {
            putchar('A' + seq[i]);
        }
        printf("\n");
    }
    return 0;
}