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Copy pathbead_sort.cpp
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75 lines (63 loc) · 2.14 KB
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/**
* bead sort
* https://en.wikipedia.org/wiki/Bead_sort
*
* 模拟珠子掉落
* 假设N个数字排序，最大数字为M，则模拟构建M条线，串上珠子。每条线的同一行对应一个待排序数字，一共N行。
* 即，如果第5个数字为3，则第五行的前三条线对应位置有珠子，其他线第五行没有珠子。串完之后，珠子随重力下落。
* 然后从各行数珠子恢复结果，则为已排序数组。
*/
#include <iostream>
#include <cstdint>
#include <cstring>
#include <vector>
void bead_sort(std::vector<int> *array) {
auto max_rows = array->size();; // make it readable
int max_cols = (*array)[0];
for (auto row = 1; row < max_rows; ++row) {
if ((*array)[row] > max_cols) {
max_cols = (*array)[row];
}
}
uint8_t *beads = new uint8_t[max_cols * max_rows];
memset(beads, 0, max_cols * max_rows);
auto get_bead_at = [&](int row, int col) {
return &beads[row * max_cols + col];
};
// construct initial beads from original array
for (auto row = 0; row < max_rows; ++row) {
for (auto col = 0; col < (*array)[row]; ++col) {
*get_bead_at(row, col) = 1;
}
}
// beads falling down
for (auto col = 0; col < max_cols; ++col) {
auto beads_in_row = 0;
for (auto row = 0; row < max_rows; ++row) {
auto *bead = get_bead_at(row, col);
beads_in_row += static_cast<int>(*bead);
*bead = 0;
}
for (auto row = max_rows - beads_in_row; row < max_rows; ++row) {
*get_bead_at(row, col) = 1;
}
}
// recover array from beads after falling down
for (auto row = 0; row < max_rows; ++row) {
auto col = 0;
// for (; col < max_cols && *get_bead_at(row, col) == 1; ++col)
while (col < max_cols && *get_bead_at(row, col) == 1) {
++col;
}
(*array)[row] = col;
}
delete [] beads;
}
int main() {
std::vector<int> array{5, 3, 1, 7, 4, 1, 1, 20};
bead_sort(&array);
for (const auto &e : array) {
std::cout << e << ", ";
}
std::cout << std::endl;
}