// Package q1536 implements a solution for https://leetcode.com/problems/minimum-swaps-to-arrange-a-binary-grid/
package q1536

func minSwaps(grid [][]int) int {
	n := len(grid)

	zeros := grid[0] // reuse memory
	for i := range grid {
		z := n - 1
		for z >= 0 && grid[i][z] == 0 {
			z--
		}
		zeros[i] = n - z - 1
	}

	steps := 0
	for row := range n - 1 {
		needZ := n - row - 1
		if zeros[row] >= needZ {
			continue
		}

		// Find a row with at lease needZ zeros at the end
		found := -1
		for i := row + 1; i < n; i++ {
			if zeros[i] >= needZ {
				found = i
				break
			}
		}
		if found == -1 {
			return -1
		}

		steps += found - row
		t := zeros[found]
		copy(zeros[row+1:found+1], zeros[row:found])
		zeros[row] = t
	}

	return steps
}

var _ = minSwaps