package main

import "fmt"

func findDiagonalOrder(mat [][]int) []int {
	if len(mat) == 0 || len(mat[0]) == 0{
		return []int{}
	}

	m := len(mat)
	n := len(mat[0])
	
	// maps
	diagonals := make(map[int][]int)

	for i:=0; i< m;i++{
		for j:=0; j < n; j++{
			index := i+j
			diagonals[index] = append(diagonals[index], mat[i][j])
		}
	}

	result := []int{}

	for i:= 0; i< m+n-1; i++{
		if i% 2 == 0{
			reverse(diagonals[i])
			result = append(result, diagonals[i]...)
		}else{
			result = append(result, diagonals[i]...)
		}
	}

	return result
}

func reverse(slice []int){
	left, right :=0, len(slice)-1

	for left < right{
		slice[left], slice[right] = slice[right], slice[left]
		left++
		right--
	}
}