[LeetCode]Number of Islands

public class Solution {
    public int numIslands(char[][] grid) {
        int row = grid.length;
        if (row == 0) {
            return 0;
        }
        int col = grid[0].length;
        int[][] record = new int[row][col];
        int result = 1;
        for (int r = 0; r < row; r++) {
            for (int c = 0; c < col; c++) {
                if (grid[r][c] == '1' && record[r][c] == 0) {
                    helper(grid, record, r, c, result++);
                }
            }
        }
        return result - 1;
    }
    public void helper(char[][] grid, int[][] record, int r, int c, int tmp) {
        record[r][c] = tmp;
        if (r > 0 && grid[r - 1][c] == '1' && record[r - 1][c] == 0) {
            helper(grid, record, r - 1, c, tmp);
        }
        if (r + 1 < grid.length && grid[r + 1][c] == '1' && record[r + 1][c] == 0) {
            helper(grid, record, r + 1, c, tmp);
        }
        if (c > 0 && grid[r][c - 1] == '1' && record[r][c - 1] == 0) {
            helper(grid, record, r, c - 1, tmp);
        }
        if (c + 1 < grid[0].length && grid[r][c + 1] == '1' && record[r][c + 1] == 0) {
            helper(grid, record, r, c + 1, tmp);
        }
    }
}

 

Union Find

public class Solution {
    private int[] array;
    private int row, col;
    public int numIslands(char[][] grid) {
        int row = grid.length;
        if (row == 0) {
            return 0;
        }
        int col = grid[0].length;
        this.row = row;
        this.col = col;
        array = new int[row * col];
        Arrays.fill(array, -1);
        for (int r = 0; r < row; r++) {
            for (int c = 0; c < col; c++) {
                int x = r * col + c;
                if (grid[r][c] == '1') {
                    if (array[x] == -1) {
                        array[x] = x;
                    }
                    if (r > 0 && grid[r - 1][c] == '1') {
                        set(r - 1, c, r, c);
                    }
                    if (r + 1 < row && grid[r + 1][c] == '1') {
                        set(r + 1, c, r, c);
                    }
                    if (c > 0 && grid[r][c - 1] == '1') {
                        set(r, c - 1, r, c);
                    }
                    if (c + 1 < col && grid[r][c + 1] == '1') {
                        set(r, c + 1, r, c);
                    }
                }
            }
        }
        int result = 0;
        for (int r = 0; r < row; r++) {
            for (int c = 0; c < col; c++) {
                int x = r * col + c;
                if (array[x] == x) {
                    result ++;
                }
            }
        }
        return result;
    }
    private int find(int x) {
        int y = array[x];
        if (y != -1 && x != y) {
            return find(y);
        }
        return y;
    }
    private void set(int r1, int c1, int r2, int c2) {
        int tmp1 = find(r1 * col + c1);
        int tmp2 = find(r2 * col + c2);
        if (tmp1 == -1) {
            array[r1 * col + c1] = tmp2;
        } else {
            array[tmp1] = tmp2;
        }
    }
}