Leetcode刷题笔记1 图论part03

卡码网 101 孤岛总面积

from collections import deque
directions = [[0, 1], [1, 0], [0, -1], [-1, 0]]
count = 0

def main():
    global count
    n, m = map(int, input().split())
    grid = []
    for _ in range(n):
        grid.append(list(map(int, input().split())))
    for i in range(n):
        if grid[i][0] == 1:
            dfs(grid, i, 0)
        if grid[i][m - 1] == 1:
            dfs(grid, i, m - 1)
    for j in range(m):
        if grid[0][j] == 1:
            dfs(grid, 0, j)
        if grid[n - 1][j] == 1:
            dfs(grid, n - 1, j)
    count = 0
    for i in range(n):
        for j in range(m):
            if grid[i][j] == 1:
                dfs(grid, i, j)
    print(count)

def dfs(grid, i, j):
    que = deque()
    global count
    que.append((i, j))
    grid[i][j] = 0
    count += 1
    while que:
        cur_x, cur_y = que.popleft()
        for x, y in directions:
            next_x, next_y = cur_x + x, cur_y + y
            if next_x < 0 or next_y < 0 or next_x >= len(grid) or next_y >= len(grid[0]):
                continue
            if grid[next_x][next_y] == 1:
                count += 1
                que.append((next_x, next_y))
                grid[next_x][next_y] = 0

if __name__ == '__main__':
    main()
    

卡码网 102 沉没孤岛

from collections import deque

n, m = list(map(int, input().split()))
g = []
for _ in range(n):
    row = list(map(int,input().split()))
    g.append(row)
    
directions = [(1,0),(-1,0),(0,1),(0,-1)]
count = 0

def bfs(r,c,mode):
    global count 
    q = deque()
    q.append((r,c))
    count += 1
    
    while q:
        r, c = q.popleft()
        if mode:
            g[r][c] = 2
            
        for di in directions:
            next_r = r + di[0]
            next_c = c + di[1]
            if next_c < 0 or next_c >= m or next_r < 0 or next_r >= n:
                continue
            if g[next_r][next_c] == 1:
                q.append((next_r,next_c))
                if mode:
                    g[r][c] = 2
                    
                count += 1
    

for i in range(n):
    if g[i][0] == 1: bfs(i,0,True)
    if g[i][m-1] == 1: bfs(i, m-1,True)
    
for j in range(m):
    if g[0][j] == 1: bfs(0,j,1)
    if g[n-1][j] == 1: bfs(n-1,j,1)

for i in range(n):
    for j in range(m):
        if g[i][j] == 2:
            g[i][j] = 1
        else:
            g[i][j] = 0
            
for row in g:
    print(" ".join(map(str, row)))

卡码网 103 水流问题

first = set()
second = set()
directions = [[0, 1], [1, 0], [0 ,-1], [-1, 0]]
def dfs(i, j, grid, visited, side):
    if visited[i][j]:
        return
    visited[i][j] = True
    side.add((i, j))
    for x, y in directions:
        new_x = i + x 
        new_y = j + y
        if (
            0 <= new_x < len(grid)
            and 0 <= new_y < len(grid[0])
            and int(grid[new_x][new_y]) >= int(grid[i][j])
        ):
            dfs(new_x, new_y, grid, visited, side)
    
def main():
    global first
    global second
    n, m = map(int, input().split())
    grid = []
    for _ in range(n):
        grid.append(list(map(int, input().strip().split())))
        
    visited = [[False] * m for _ in range(n)]
    for i in range(m):
        dfs(0, i, grid, visited, first)
    for i in range(n):
        dfs(i, 0, grid, visited, first)
    visited = [[False] * m for _ in range(n)]
    for i in range(m):
        dfs(n - 1, i, grid, visited, second)
    for i in range(n):
        dfs(i, m - 1, grid, visited, second)
    res = first & second
    for x, y in res:
        print(f"{x} {y}")
 
if __name__ == '__main__':
    main()

卡码网 104 建造最大岛屿

from typing import List 
from collections import defaultdict

class Solution():
    def __init__(self):
        self.direction = [[0, 1], [1, 0], [0, -1], [-1, 0]]
        self.res = 0
        self.count = 0
        self.idx = 1
        self.count_area = defaultdict(int)

    def max_area_island(self, grid: List[List[int]]) -> int:
        if not grid or len(grid) == 0 or len(grid[0]) == 0:
            return 0
        for i in range(len(grid)):
            for j in range(len(grid[0])):
                if grid[i][j] == 1:
                    self.count = 0
                    self.idx += 1
                    self.dfs(grid, i, j)
        self.check_area(grid)
        if self.check_largest_connnect_island(grid):
            return self.res + 1
        return max(self.count_area.values())
    
    def dfs(self, grid, x, y):
        grid[x][y] = self.idx
        self.count += 1
        for i, j in self.direction:
            next_x = x + i
            next_y = y + j
            if 0 <= next_x < len(grid) and 0 <= next_y < len(grid[0]) and grid[next_x][next_y] == 1:
                self.dfs(grid, next_x, next_y)
        return
    
    def check_area(self, grid):
        for i in range(len(grid)):
            for j in range(len(grid[0])):
                self.count_area[grid[i][j]] = self.count_area.get(grid[i][j], 0) + 1
        return

    def check_largest_connnect_island(self, grid):
        m, n = len(grid), len(grid[0])
        has_connect = False
        for i in range(m):
            for j in range(n):
                if grid[i][j] == 0:
                    has_connect = True
                    area = 0
                    visited = set()
                    for x, y in self.direction:
                        next_x = x + i
                        next_y = y + j
                        if 0 <= next_x < len(grid) and 0 <= next_y < len(grid[0]) and grid[next_x][next_y] != 0 and grid[next_x][next_y] not in visited:
                            visited.add(grid[next_x][next_y])
                            area += self.count_area[grid[next_x][next_y]]
                            self.res = max(self.res, area)
        return has_connect

def main():
    n, m = map(int, input().split())
    grid = []
    for _ in range(n):
        grid.append(list(map(int, input().strip().split())))
    sol = Solution()
    print(sol.max_area_island(grid))
if __name__ == '__main__':
    main()