README_EN.md

959. Regions Cut By Slashes

中文文档

Description

An n x n grid is composed of 1 x 1 squares where each 1 x 1 square consists of a '/', '\', or blank space ' '. These characters divide the square into contiguous regions.

Given the grid grid represented as a string array, return the number of regions.

Note that backslash characters are escaped, so a '\' is represented as '\\'.

 

Example 1:

Input: grid = [" /","/ "]
Output: 2

Example 2:

Input: grid = [" /","  "]
Output: 1

Example 3:

Input: grid = ["/\\","\\/"]
Output: 5
Explanation: Recall that because \ characters are escaped, "\\/" refers to \/, and "/\\" refers to /\.

 

Constraints:

• n == grid.length == grid[i].length
• 1 <= n <= 30
• grid[i][j] is either '/', '\', or ' '.

Solutions

Python3

class Solution:
    def regionsBySlashes(self, grid: List[str]) -> int:
        def find(x):
            if p[x] != x:
                p[x] = find(p[x])
            return p[x]

        def union(a, b):
            pa, pb = find(a), find(b)
            if pa != pb:
                p[pa] = pb
                nonlocal size
                size -= 1

        n = len(grid)
        size = n * n * 4
        p = list(range(size))
        for i, row in enumerate(grid):
            for j, v in enumerate(row):
                k = i * n + j
                if i < n - 1:
                    union(4 * k + 2, (k + n) * 4)
                if j < n - 1:
                    union(4 * k + 1, (k + 1) * 4 + 3)
                if v == '/':
                    union(4 * k, 4 * k + 3)
                    union(4 * k + 1, 4 * k + 2)
                elif v == '\\':
                    union(4 * k, 4 * k + 1)
                    union(4 * k + 2, 4 * k + 3)
                else:
                    union(4 * k, 4 * k + 1)
                    union(4 * k + 1, 4 * k + 2)
                    union(4 * k + 2, 4 * k + 3)
        return size

Java

class Solution {
    private int[] p;
    private int size;

    public int regionsBySlashes(String[] grid) {
        int n = grid.length;
        size = n * n * 4;
        p = new int[size];
        for (int i = 0; i < p.length; ++i) {
            p[i] = i;
        }
        for (int i = 0; i < n; ++i) {
            for (int j = 0; j < n; ++j) {
                int k = i * n + j;
                if (i < n - 1) {
                    union(4 * k + 2, (k + n) * 4);
                }
                if (j < n - 1) {
                    union(4 * k + 1, (k + 1) * 4 + 3);
                }
                char v = grid[i].charAt(j);
                if (v == '/') {
                    union(4 * k, 4 * k + 3);
                    union(4 * k + 1, 4 * k + 2);
                } else if (v == '\\') {
                    union(4 * k, 4 * k + 1);
                    union(4 * k + 2, 4 * k + 3);
                } else {
                    union(4 * k, 4 * k + 1);
                    union(4 * k + 1, 4 * k + 2);
                    union(4 * k + 2, 4 * k + 3);
                }
            }
        }
        return size;
    }

    private int find(int x) {
        if (p[x] != x) {
            p[x] = find(p[x]);
        }
        return p[x];
    }

    private void union(int a, int b) {
        int pa = find(a);
        int pb = find(b);
        if (pa == pb) {
            return;
        }
        p[pa] = pb;
        --size;
    }
}

C++

class Solution {
public:
    vector<int> p;
    int size;

    int regionsBySlashes(vector<string>& grid) {
        int n = grid.size();
        size = n * n * 4;
        p.resize(size);
        for (int i = 0; i < size; ++i) p[i] = i;
        for (int i = 0; i < n; ++i) {
            for (int j = 0; j < n; ++j) {
                int k = i * n + j;
                if (i < n - 1) merge(4 * k + 2, (k + n) * 4);
                if (j < n - 1) merge(4 * k + 1, (k + 1) * 4 + 3);
                char v = grid[i][j];
                if (v == '/') {
                    merge(4 * k, 4 * k + 3);
                    merge(4 * k + 1, 4 * k + 2);
                } else if (v == '\\') {
                    merge(4 * k, 4 * k + 1);
                    merge(4 * k + 2, 4 * k + 3);
                } else {
                    merge(4 * k, 4 * k + 1);
                    merge(4 * k + 1, 4 * k + 2);
                    merge(4 * k + 2, 4 * k + 3);
                }
            }
        }
        return size;
    }

    void merge(int a, int b) {
        int pa = find(a);
        int pb = find(b);
        if (pa == pb) return;
        p[pa] = pb;
        --size;
    }

    int find(int x) {
        if (p[x] != x) p[x] = find(p[x]);
        return p[x];
    }
};

Go

func regionsBySlashes(grid []string) int {
	n := len(grid)
	size := n * n * 4
	p := make([]int, size)
	for i := range p {
		p[i] = i
	}
	var find func(x int) int
	find = func(x int) int {
		if p[x] != x {
			p[x] = find(p[x])
		}
		return p[x]
	}
	union := func(a, b int) {
		pa, pb := find(a), find(b)
		if pa == pb {
			return
		}
		p[pa] = pb
		size--
	}
	for i, row := range grid {
		for j, v := range row {
			k := i*n + j
			if i < n-1 {
				union(4*k+2, (k+n)*4)
			}
			if j < n-1 {
				union(4*k+1, (k+1)*4+3)
			}
			if v == '/' {
				union(4*k, 4*k+3)
				union(4*k+1, 4*k+2)
			} else if v == '\\' {
				union(4*k, 4*k+1)
				union(4*k+2, 4*k+3)
			} else {
				union(4*k, 4*k+1)
				union(4*k+1, 4*k+2)
				union(4*k+2, 4*k+3)
			}
		}
	}
	return size
}

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