package main
import (
"fmt"
)
// A sparse matrix is a matrix in which the majority of elements are zero.
// To rebuild a sparse matrix from a compact (triplet) representation,
// we create a full matrix initialized with zeros, then place each
// non‑zero element at its (row, column) position.
// Build full sparse matrix from compact triplet form
func buildSparseFromCompact(compact [][]int, count int) [][]int {
rowIdx := compact[0]
colIdx := compact[1]
values := compact[2]
// Determine matrix dimensions automatically
maxRow := 0
maxCol := 0
for i := 0; i < count; i++ {
if rowIdx[i] > maxRow {
maxRow = rowIdx[i]
}
if colIdx[i] > maxCol {
maxCol = colIdx[i]
}
}
rows := maxRow + 1
cols := maxCol + 1
// Create full matrix initialized with zeros
sparse := make([][]int, rows)
for i := range sparse {
sparse[i] = make([]int, cols)
}
// Fill matrix
for i := 0; i < count; i++ {
sparse[rowIdx[i]][colIdx[i]] = values[i]
}
return sparse
}
// Print a matrix
func printMatrix(mat [][]int, title string) {
fmt.Println(title)
for _, row := range mat {
for _, x := range row {
fmt.Printf("%d ", x)
}
fmt.Println()
}
fmt.Println()
}
func main() {
// Compact matrix:
// 0 0 1 1 1 3 3 3 4
// 2 4 2 3 6 1 2 5 4
// 3 8 5 7 1 2 6 4 9
compact := [][]int{
{0, 0, 1, 1, 1, 3, 3, 3, 4}, // row indices
{2, 4, 2, 3, 6, 1, 2, 5, 4}, // column indices
{3, 8, 5, 7, 1, 2, 6, 4, 9}, // values
}
count := 9
fmt.Println("Compact matrix:")
for i := 0; i < 3; i++ {
for j := 0; j < count; j++ {
fmt.Printf("%d ", compact[i][j])
}
fmt.Println()
}
fmt.Println()
sparse := buildSparseFromCompact(compact, count)
printMatrix(sparse, "Sparse matrix (auto-sized):")
}
/*
run:
Compact matrix:
0 0 1 1 1 3 3 3 4
2 4 2 3 6 1 2 5 4
3 8 5 7 1 2 6 4 9
Sparse matrix (auto-sized):
0 0 3 0 8 0 0
0 0 5 7 0 0 1
0 0 0 0 0 0 0
0 2 6 0 0 4 0
0 0 0 0 9 0 0
*/
