提出 #16587795

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ソースコード 拡げる

import sys

sys.path.append("/home/contestant/.local/lib/python3.8/site-packages")


import networkx as nx

R, C = [int(x) for x in input().split()]
grid = [list(input()) for r in range(R)]


def pack(r, c):
    return r * C + c


graph = nx.Graph()
top_nodes = set()  # top half of the bipartite graph
for r in range(R):
    for c in range(C):
        if r + 1 < R and grid[r][c] == grid[r + 1][c] == ".":
            u, v = pack(r, c), pack(r + 1, c)
            graph.add_edge(u, v)
            if (r + c) % 2 == 0:
                top_nodes.add(v)
            else:
                top_nodes.add(u)
        if c + 1 < C and grid[r][c] == grid[r][c + 1] == ".":
            u, v = pack(r, c), pack(r, c + 1)
            graph.add_edge(u, v)
            if (r + c) % 2 == 0:
                top_nodes.add(v)
            else:
                top_nodes.add(u)


matching = nx.bipartite.maximum_matching(graph, top_nodes=top_nodes)

count = 0
for u, v in matching.items():
    if u > v:
        assert matching[v] == u
        r1, c1 = divmod(u, C)
        r2, c2 = divmod(v, C)
        if r1 == r2:
            if c1 > c2:
                c1, c2 = c2, c1
            grid[r1][c1], grid[r2][c2] = ">", "<"
        elif c1 == c2:
            if r1 > r2:
                r1, r2 = r2, r1
            grid[r1][c1] = "v"
            grid[r2][c2] = "^"
        count += 1

print(count)
for row in grid:
    print("".join(row))

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