River Sizes Problem

Program.kt

package com.algoexpert.program

fun riverSizes(matrix: List<List<Int>>): List<Int> {
	val m = matrix
		.map { it.toMutableList() }
		.toMutableList()
	
	fun size(i: Int, j: Int): Int {
		if (i < 0 || i >= m.size ||
			j < 0 || j >= m[i].size ||
			m[i][j] == 0) {
			return 0
		}
		m[i][j] = 0
		
		return 1 + size(i + 1, j) + 
				   size(i - 1, j) + 
				   size(i, j + 1) + 
				   size(i, j - 1) 
		
	}
	val result = mutableListOf<Int>()
	
	for(i in m.indices){
		for(j in m[i].indices){
			var s = size(i, j)
			if (s > 0) {
				result.add(s)
			}
		}
	}
    return result
}