130, Surrounded regions

130, Surrounded regions

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DFS boundary

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1. 題目是說被1包圍的0 可以被翻牌

=>

沒有碰到邊界的0 可以被翻牌

（有連結到）碰到邊界的0無法被翻牌

2. 從邊界開始找有沒有0

當找到邊界為0, 對它的做DFS(上下左右)

找到的0, 先把它變更符號e.g.#

3. for, for go through

剩下的0是可以翻成1的

剩下的#是不能翻的 翻回0

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class Solution{

public:

  void surroundRegion(vec<vec<char>>&board){

    int m=board.size(), n=board[0].size()

    for int i=0; i<m; i++

      if board[i][0] == 'o'

        DFS(board, i, 0, m, n)

      if board[i][n-1] == 'o'

        DFS(board, i, n-1, m, n)

    for int j=0; j<n; j++

      if board[0][j] == 'o'

        DFS(board, 0, j, m, n)

      if board[m-1] == 'o'

        DFS(board, m-1, j, m, n)

    for i-n

      for j-n

        if board[i][j] == 'o'

          board[i][j] = 'x'

        if board[i][j] == '#'

          board[i][j] = 'o'

}

void DFS(vec<vec<char>>board, int i, j, m, n){

  if i<0 || j<0 || i>=m || j>=n || board(i,j)!='o'

    return

  board(i,j) = '#'

  DFS(i-1, j, m, n)

  DFS(i+1, j, m, n)

  DFS(i, j-1, m, n)

  DFS(I, j+1, m, n

}