为什么top.x加的是纵坐标对应的数组top.y加的是横坐标

#include<bits/stdc++.h>

#define IOS ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);

using namespace std;

const int N = 2e3 + 5;

const int INF = 0x7f7f7f7f;

struct Node {

int x;

int y;

} node;

int a[N][N],p[N][N];

int b[3] = {-1,1,0};

int c[3] = {0,0,1};

int n,m;

int bfs() {

queue<Node> qu;

node.x = 1;

node.y = 1;

qu.push(node);

while(!qu.empty()) {

Node top = qu.front();

qu.pop();

for(int i = 0; i < 3; i++) {

int newx = top.x + b[i];

int newy = top.y + c[i];

if(newx < 1 || newx > n || newy < 1 || newy > m)

continue;

int d = (a[top.x][top.y] == a[newx][newy] ? 1 : 2);

if(p[newx][newy] > p[top.x][top.y] + d) {

p[newx][newy] = p[top.x][top.y] + d;

node.x = newx;

node.y = newy;

qu.push(node);

}

}

}

return p[n][m];

}

int main() {

IOS

cin >> n >> m;

for(int i = 1; i <= n; i++)

for(int j = 1; j <= m; j++)

cin >> a[i][j];

memset(p,0x3f,sizeof(p));

p[1][1] = 0;

cout << bfs();

return 0;

}