542_01_matrix

class Solution(object):
    def updateMatrix(self, matrix):
        """
        :type matrix: List[List[int]]
        :rtype: List[List[int]]
        """
        R, C = len(matrix), len(matrix[0])
        rtn = matrix
        
        def bfs(r,c):
            toCheck = [[r, c]]
            cnt = -1
            while toCheck:
                cnt += 1
                temp = []
                for m, n in toCheck:
                    if matrix[m][n] == 0: 
                        rtn[r][c] = cnt
                        return
                    if m-1>=0 :temp.append([m-1,n])
                    if n-1>=0 :temp.append([m,n-1])
                    if m<R-1 :temp.append([m+1,n])
                    if n<C-1 :temp.append([m,n+1])
                toCheck = temp
            
                 
        for r in range(R):
            for c in range(C):
                bfs(r, c)
        
        return rtn