带记录方向的DFS

#include<bits/stdc++.h>
using namespace std;
#define ioio ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define endl "\n"
#define debug(x) cout<<#x<<":"<<x<<endl;
#define L(k) k<<1
#define R(k) k<<1|1
#define P pair
#define P1 first
#define P2 second
#define u_map unordered_map
#define p_queue priority_queue
typedef long long ll;
const double eps = 1e-6;
const int mod = 1e9 + 7;
const int INF = 0x3f3f3f3f;
const int INF2 = (1 << 31);
const int N = 2e2 + 7;
int dx[] = {1, 0, -1, 0}, dy[] = {0, -1, 0, 1};
/*-------------------------------------------------*/

int n,m;
int ma[N][N];
bool vis[N][N];
vector<int>v;

void dfs(int x,int y,int pre){
	v.push_back(ma[x][y]);
	vis[x][y]=1;
	for(int i=pre,flag=0;i<=4;i++){
		if(flag==1&&i==4)break;
		else if(i==4){
			i=0;
			flag=1;
		}
		int xx=x+dx[i];
		int yy=y+dy[i];
		if(xx>=1&&xx<=n&&yy>=1&&yy<=m&&vis[xx][yy]==0){
			dfs(xx,yy,i);
			break;
		}
	}
}
void slove() {
	cin>>n>>m;
	for(int i=1;i<=n;i++)
		for(int j=1;j<=m;j++)
			cin>>ma[i][j];
	dfs(1,1,0);
	for(int x:v)
		cout<<x<<" ";
}
int main() {
	ioio
	int t=1;
	//freopen("./test.txt","r",stdin);
	//cin>>t;
	while(t--)
		slove();
	return 0;
}

① 改变方向条件,越界或者已经访问过了，访问过就用vis数组记录为1

② 如果遍历四个方向，如果四个方向都走完都没有路可以走，就break;

易错点：不能把访问过的数字记录成0,因为矩阵里面可能有0的存在。（整了好久，才发现）

代码：

#include <bits/stdc++.h>
using namespace std;
int n, m, a[205][205], D[4][2] = {{1, 0}, {0, 1}, {-1, 0}, {0, -1}};
bool vis[205][205];
int main() {
	scanf("%d%d", &m, &n);
	for (int i = 1; i <= m; ++i)
		for (int j = 1; j <= n; ++j)
			scanf("%d", &a[i][j]);
	int k = 0, num = 0, x = 1, y = 1;
	printf("%d ", a[x][y]);
	vis[x][y] = 1;
	while (true) {
		int xx = x + D[k][0], yy = y + D[k][1];
		while ((xx < 1 || xx > m || yy < 1 || yy > n || vis[xx][yy]) && num < 5) {
			k += 1;
			k %= 4;
			xx = x + D[k][0], yy = y + D[k][1];
			num += 1;
		}
		if (num >= 5)
			break;
		x = xx, y = yy;
		printf("%d ", a[xx][yy]);
		vis[xx][yy] = 1;
		num = 0;
	} 	
	return 0;
}

代码很好懂

#include<iostream>
#include<cstdio>
#include<cmath>
#include<cstdlib>
#include<cstring>
#include<algorithm>
#include<vector>
#include<string>
#include<map>
#include <climits>

using namespace std;

int  num[205][205];
bool numi[205][205];
int main(void)
{
	int a, b;
	cin >> a >> b;

	int k = a * b;
	for(int i=0;i<a;i++)
		for (int t = 0; t < b; t++) 
		{
			cin >> num[i][t];
			numi[i][t] = true;
		}
	int x = 0, y = 0;
	
	while (k)
	{
		for (int i = y; i < a; i++)
		{
			if (!numi[i][x]) break;
			y = i;
			k--;
			numi[i][x] = false;
			k != 0 ? cout << num[i][x] << " " : cout << num[i][x];
		}
		if (!k) break;
		x++;
		for (int i = x; i < b; i++)
		{
			if (!numi[y][i]) break;
			x = i;
			k--;
			numi[y][i] = false;
			k != 0 ? cout << num[y][i] << " " : cout << num[y][i];
		}
		if (!k) break;
		y--;
		for (int i = y; i >= 0; i--)
		{
			if (!numi[i][x]) break;
			y = i;
			k--;
			numi[i][x] = false;
			k != 0 ? cout << num[i][x] << " " : cout << num[i][x];
		}
		if (!k) break;
		x--;
		for (int i = x; i >= 0; i--)
		{
			if (!numi[y][i]) break;
			x = i;		
			k--;
			numi[y][i] = false;
			k != 0 ? cout << num[y][i] << " " : cout << num[y][i];
		}
		if (!k) break;
		y++;
	}

	return 0;
}