给定大小为N * M的网格仅包含0和1 ，任务是查找给定网格中连接的最长1的长度。我们只能从网格的任何当前单元格向左，向右，向上或向下移动。
例子：
Input: N = 3, M = 3, grid[][] = { {0, 0, 0}, {0, 1, 0}, {0, 0, 0} }
Output: 1
Explanation:
The longest possible route is 1 as there cant be any movement from (1, 1) position of the matrix.
Input: N = 6, M = 7, grid[][] = { {0, 0, 0, 0, 0, 0, 0}, {0, 1, 0, 1, 0, 0, 0}, {0, 1, 0, 1, 0, 0, 0}, {0, 1, 0, 1, 0, 1, 0}, {0, 1, 1, 1, 1, 1, 0}, {0, 0, 0, 0, 0, 0, 0}}
Output: 9
Explanation:
The longest possible route is 9 starting from (1, 1) -> (2, 1) -> (3, 1) -> (4, 1) -> (4, 2) -> (4, 3) -> (4, 4) -> (4, 5) -> (3, 5).
方法：想法是在当前单元格值为1的网格上进行DFS遍历，并递归调用当前单元格的所有四个方向，其中值为1并更新连接的最大长度1 。
下面是上述方法的实现：
C++
// C++ program for the above approach
#include
#define row 6
#define col 7
using namespace std;
int vis[row + 1][col + 1], id;
int diameter = 0, length = 0;
// Keeps a track of directions
// that is up, down, left, right
int dx[] = { -1, 1, 0, 0 };
int dy[] = { 0, 0, -1, 1 };
// Function to perform the dfs traversal
void dfs(int a, int b, int lis[][col],
int& x, int& y)
{
// Mark the current node as visited
vis[a][b] = id;
// Increment length from this node
length++;
// Update the diameter length
if (length > diameter) {
x = a;
y = b;
diameter = length;
}
for (int j = 0; j < 4; j++) {
// Move to next cell in x-direction
int cx = a + dx[j];
// Move to next cell in y-direction
int cy = b + dy[j];
// Check if cell is invalid
// then continue
if (cx < 0 || cy < 0 || cx >= row
|| cy >= col || lis[cx][cy] == 0
|| vis[cx][cy]) {
continue;
}
// Perform DFS on new cell
dfs(cx, cy, lis, x, y);
}
vis[a][b] = 0;
// Decrement the length
length--;
}
// Function to find the maximum length of
// connected 1s in the given grid
void findMaximumLength(int lis[][col])
{
int x, y;
// Increment the id
id++;
length = 0;
diameter = 0;
// Traverse the grid[]
for (int i = 0; i < row; i++) {
for (int j = 0; j < col; j++) {
if (lis[i][j] != 0) {
// Find start point of
// start dfs call
dfs(i, j, lis, x, y);
i = row;
break;
}
}
}
id++;
length = 0;
diameter = 0;
// DFS Traversal from cell (x, y)
dfs(x, y, lis, x, y);
// Print the maximum length
cout << diameter;
}
// Driver Code
int main()
{
// Given grid[][]
int grid[][col] = { { 0, 0, 0, 0, 0, 0, 0 },
{ 0, 1, 0, 1, 0, 0, 0 },
{ 0, 1, 0, 1, 0, 0, 0 },
{ 0, 1, 0, 1, 0, 1, 0 },
{ 0, 1, 1, 1, 1, 1, 0 },
{ 0, 0, 0, 1, 0, 0, 0 } };
// Function Call
findMaximumLength(grid);
return 0;
} Java
// Java program for the above approach
import java.util.*;
class GFG{
static final int row = 6;
static final int col = 7;
static int [][]vis = new int[row + 1][col + 1];
static int id;
static int diameter = 0, length = 0;
static int x = 0, y = 0;
// Keeps a track of directions
// that is up, down, left, right
static int dx[] = { -1, 1, 0, 0 };
static int dy[] = { 0, 0, -1, 1 };
// Function to perform the dfs traversal
static void dfs(int a, int b, int lis[][])
{
// Mark the current node as visited
vis[a][b] = id;
// Increment length from this node
length++;
// Update the diameter length
if (length > diameter)
{
x = a;
y = b;
diameter = length;
}
for(int j = 0; j < 4; j++)
{
// Move to next cell in x-direction
int cx = a + dx[j];
// Move to next cell in y-direction
int cy = b + dy[j];
// Check if cell is invalid
// then continue
if (cx < 0 || cy < 0 ||
cx >= row || cy >= col ||
lis[cx][cy] == 0 || vis[cx][cy] > 0)
{
continue;
}
// Perform DFS on new cell
dfs(cx, cy, lis);
}
vis[a][b] = 0;
// Decrement the length
length--;
}
// Function to find the maximum length of
// connected 1s in the given grid
static void findMaximumLength(int lis[][])
{
// Increment the id
id++;
length = 0;
diameter = 0;
// Traverse the grid[]
for(int i = 0; i < row; i++)
{
for(int j = 0; j < col; j++)
{
if (lis[i][j] != 0)
{
// Find start point of
// start dfs call
dfs(i, j, lis);
i = row;
break;
}
}
}
id++;
length = 0;
diameter = 0;
// DFS Traversal from cell (x, y)
dfs(x, y, lis);
// Print the maximum length
System.out.print(diameter);
}
// Driver Code
public static void main(String[] args)
{
// Given grid[][]
int grid[][] = { { 0, 0, 0, 0, 0, 0, 0 },
{ 0, 1, 0, 1, 0, 0, 0 },
{ 0, 1, 0, 1, 0, 0, 0 },
{ 0, 1, 0, 1, 0, 1, 0 },
{ 0, 1, 1, 1, 1, 1, 0 },
{ 0, 0, 0, 1, 0, 0, 0 } };
// Function Call
findMaximumLength(grid);
}
}
// This code is contributed by amal kumar choubeyPython3
# Python3 program for the above approach
row = 6
col = 7
vis = [[0 for i in range(col + 1)]
for j in range(row + 1)]
id = 0
diameter = 0
length = 0
# Keeps a track of directions
# that is up, down, left, right
dx = [ -1, 1, 0, 0 ]
dy = [ 0, 0, -1, 1 ]
# Function to perform the dfs traversal
def dfs(a, b, lis, x, y):
global id, length, diameter
# Mark the current node as visited
vis[a][b] = id
# Increment length from this node
length += 1
# Update the diameter length
if (length > diameter):
x = a
y = b
diameter = length
for j in range(4):
# Move to next cell in x-direction
cx = a + dx[j]
# Move to next cell in y-direction
cy = b + dy[j]
# Check if cell is invalid
# then continue
if (cx < 0 or cy < 0 or
cx >= row or cy >= col or
lis[cx][cy] == 0 or vis[cx][cy]):
continue
# Perform DFS on new cell
dfs(cx, cy, lis, x, y)
vis[a][b] = 0
# Decrement the length
length -= 1
return x, y
# Function to find the maximum length of
# connected 1s in the given grid
def findMaximumLength(lis):
global id, length, diameter
x = 0
y = 0
# Increment the id
id += 1
length = 0
diameter = 0
# Traverse the grid[]
for i in range(row):
for j in range(col):
if (lis[i][j] != 0):
# Find start point of
# start dfs call
x, y = dfs(i, j, lis, x, y)
i = row
break
id += 1
length = 0
diameter = 0
# DFS Traversal from cell (x, y)
x, y = dfs(x, y, lis, x, y)
# Print the maximum length
print(diameter)
# Driver Code
if __name__=="__main__":
# Given grid[][]
grid = [ [ 0, 0, 0, 0, 0, 0, 0 ],
[ 0, 1, 0, 1, 0, 0, 0 ],
[ 0, 1, 0, 1, 0, 0, 0 ],
[ 0, 1, 0, 1, 0, 1, 0 ],
[ 0, 1, 1, 1, 1, 1, 0 ],
[ 0, 0, 0, 1, 0, 0, 0 ] ]
# Function Call
findMaximumLength(grid)
# This code is contributed by rutvik_56C#
// C# program for the above approach
using System;
class GFG{
static readonly int row = 6;
static readonly int col = 7;
static int [,]vis = new int[row + 1, col + 1];
static int id;
static int diameter = 0, length = 0;
static int x = 0, y = 0;
// Keeps a track of directions
// that is up, down, left, right
static int []dx = { -1, 1, 0, 0 };
static int []dy = { 0, 0, -1, 1 };
// Function to perform the dfs traversal
static void dfs(int a, int b, int [,]lis)
{
// Mark the current node as visited
vis[a, b] = id;
// Increment length from this node
length++;
// Update the diameter length
if (length > diameter)
{
x = a;
y = b;
diameter = length;
}
for(int j = 0; j < 4; j++)
{
// Move to next cell in x-direction
int cx = a + dx[j];
// Move to next cell in y-direction
int cy = b + dy[j];
// Check if cell is invalid
// then continue
if (cx < 0 || cy < 0 ||
cx >= row || cy >= col ||
lis[cx, cy] == 0 || vis[cx, cy] > 0)
{
continue;
}
// Perform DFS on new cell
dfs(cx, cy, lis);
}
vis[a, b] = 0;
// Decrement the length
length--;
}
// Function to find the maximum length of
// connected 1s in the given grid
static void findMaximumLength(int [,]lis)
{
// Increment the id
id++;
length = 0;
diameter = 0;
// Traverse the grid[]
for(int i = 0; i < row; i++)
{
for(int j = 0; j < col; j++)
{
if (lis[i, j] != 0)
{
// Find start point of
// start dfs call
dfs(i, j, lis);
i = row;
break;
}
}
}
id++;
length = 0;
diameter = 0;
// DFS Traversal from cell (x, y)
dfs(x, y, lis);
// Print the maximum length
Console.Write(diameter);
}
// Driver Code
public static void Main(String[] args)
{
// Given grid[,]
int [,]grid = { { 0, 0, 0, 0, 0, 0, 0 },
{ 0, 1, 0, 1, 0, 0, 0 },
{ 0, 1, 0, 1, 0, 0, 0 },
{ 0, 1, 0, 1, 0, 1, 0 },
{ 0, 1, 1, 1, 1, 1, 0 },
{ 0, 0, 0, 1, 0, 0, 0 } };
// Function Call
findMaximumLength(grid);
}
}
// This code is contributed by amal kumar choubey输出：
9
时间复杂度： O(行+列)