给定一个矩阵/图形/多维数组的输入(不太确定这些在编程中是否有唯一的定义),下面的函数应该输出最大岛屿的大小。陆地用 1 表示,水用 0 表示,两个有陆地的区域只有在水平或垂直(不是对 Angular 线)相邻时才连接。
下面的算法有效,但只有当我将所有岛屿保存在数组中时才是“islands”变量,然后返回保存的最大值。
最初,我试图仅跟踪“最大”变量的最大值的大小。然而,由于某种原因,它不断被重置为初始值 0。
为什么会发生这种情况?我特别困惑为什么这种情况会发生在“最大”变量而不是“岛屿”变量上,因为两者似乎具有完全相同的范围。
const bigIsland = matrix => {
let biggest = 0
let islands = []
let visited = matrix.map(row => row.map(node => false))
for(let y=0; y<matrix.length; y++){
for(let x=0; x<matrix[y].length; x++){
if (visited[y][x]) continue
checkIsland(matrix, visited, y, x, islands, biggest)
}
}
return Math.max(...islands)
}
const checkIsland = (matrix, visited, y, x, islands, biggest) => {
console.log("biggestStart", biggest)
console.log("islandsStart", islands)
let currIsland = 0
let nodesToCheck = [[y,x]]
while(nodesToCheck.length){
const [y, x] = nodesToCheck.pop()
if (visited[y][x]) continue
visited[y][x] = true
if (matrix[y][x]===0) continue
currIsland++
console.log("currIsland", currIsland)
getValidNeighbors(matrix, visited, y, x, nodesToCheck)
}
if (currIsland > biggest) biggest = currIsland
if (currIsland > 0) islands.push(currIsland)
console.log("biggest", biggest)
console.log("islands", islands)
}
const getValidNeighbors = (matrix, visited, y, x, nodesToCheck) => {
if(y>0) nodesToCheck.push([y-1, x])
if(y<matrix.length-1) nodesToCheck.push([y+1, x])
if(x>0) nodesToCheck.push([y, x-1])
if(x<matrix[y].length-1) nodesToCheck.push([y, x+1])
}
bigIsland([ [1, 0, 1],
[1, 0, 1],
[1, 0, 0] ])
最佳答案
当您将原始变量传递给函数时(例如将 biggest
传递给 checkIsland
),该函数中的任何内容都无法更改原始引用到调用函数中的该变量。为了更改 bigIsland
中的 biggest
,您需要从 checkIsland
显式返回找到的 biggest
:
const bigIsland = matrix => {
let biggest = 0
let islands = []
let visited = matrix.map(row => row.map(node => false))
for(let y=0; y<matrix.length; y++){
for(let x=0; x<matrix[y].length; x++){
if (visited[y][x]) continue
biggest = checkIsland(matrix, visited, y, x, islands, biggest)
}
}
return Math.max(...islands)
}
const checkIsland = (matrix, visited, y, x, islands, biggest) => {
console.log("biggestStart", biggest)
console.log("islandsStart", islands)
let currIsland = 0
let nodesToCheck = [[y,x]]
while(nodesToCheck.length){
const [y, x] = nodesToCheck.pop()
if (visited[y][x]) continue
visited[y][x] = true
if (matrix[y][x]===0) continue
currIsland++
console.log("currIsland", currIsland)
getValidNeighbors(matrix, visited, y, x, nodesToCheck)
}
if (currIsland > biggest) biggest = currIsland
if (currIsland > 0) islands.push(currIsland)
console.log("biggest", biggest)
console.log("islands", islands)
return biggest;
}
const getValidNeighbors = (matrix, visited, y, x, nodesToCheck) => {
if(y>0) nodesToCheck.push([y-1, x])
if(y<matrix.length-1) nodesToCheck.push([y+1, x])
if(x>0) nodesToCheck.push([y, x-1])
if(x<matrix[y].length-1) nodesToCheck.push([y, x+1])
}
bigIsland([ [1, 0, 1],
[1, 0, 1],
[1, 0, 0] ])
另一方面,当你传递islands
时,islands
是一个数组,它是一个对象(非原始),所以当islands
在checkIsland
内部发生突变时,它的变化也将在其他地方可见。引用非基元的变量本质上是对内存中对象的内存位置的引用 - 对象在传递时不会被复制,除非您明确这样做。
关于javascript - JS 为什么整型变量被重置为初始值,而数组变量却没有?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/51219309/