Increment Submatrices by One — Python

# Time:  O(q + n^2)
# Space: O(1)

# line sweep, difference matrix (2d difference array)
class Solution(object):
    def rangeAddQueries(self, n, queries):
        """
        :type n: int
        :type queries: List[List[int]]
        :rtype: List[List[int]]
        """
        result = [[0]*n for _ in xrange(n)]
        for r1, c1, r2, c2 in queries:
            result[r1][c1] += 1
            if c2+1 < len(result[0]):
                result[r1][c2+1] -= 1
            if r2+1 < len(result):
                result[r2+1][c1] -= 1
            if r2+1 < len(result) and c2+1 < len(result[0]):
                result[r2+1][c2+1] += 1
        for r in xrange(len(result)):
            for c in xrange(len(result[0])-1):
                result[r][c+1] += result[r][c]
        for r in xrange(len(result)-1):
            for c in xrange(len(result[0])):
                result[r+1][c] += result[r][c]
        return result