Matrix

Spiral Matrix

• Use dir to indicate direction 0,1,2,3
• Use rLow, rHigh and cLow, cHigh to mark range

Pascal's triangle II

• Create an array of size n and set arr[0] = 1
• We use the same array to calculate each row
• for each row, we start from the last element
• arr[j] += arr[j-1];

  1        arr = [1,0,0,0...]
  1 1      arr = [1,1,0,0...]
  1 2 1    arr = [1,2,1,0...]
  ...
  

Minesweeper

• Because the click position will always be an unrevealed square (M or E), we can igore the other cases.
• If the click position is M, then we just need to change it to revealed mine X.
• If the click position is E, we need to figure out the number of adjacent mines. There are two cases
• First, there's more than one adjacent mine, we just need to change the square to digit
• Second, there's no adjacent mine, then we can change the square to B. And do a DFS for all of its neighbors.
• Since we change E to B before DFS, so we don't need to pass a visited array.