Python 2D binary indexed tree

  • 6

    Translated this java solution

    class NumMatrix(object):
    def __init__(self, matrix):
        if not matrix:
        self.m, self.n = len(matrix), len(matrix[0])
        self.matrix, self.bit = [[0]*(self.n) for _ in range(self.m)], [[0]*(self.n+1) for _ in range(self.m+1)]
        for i in range(self.m):
            for j in range(self.n):
                self.update(i, j, matrix[i][j])
    def update(self, row, col, val):
        diff, self.matrix[row][col], i = val-self.matrix[row][col], val, row+1
        while i <= self.m:
            j = col+1
            while j <= self.n:
                self.bit[i][j] += diff
                j += (j & -j)
            i += (i & -i)
    def sumRegion(self, row1, col1, row2, col2):
        return self.sumCorner(row2, col2) + self.sumCorner(row1-1, col1-1) - self.sumCorner(row1-1, col2) - self.sumCorner(row2, col1-1)
    def sumCorner(self, row, col):
        res, i = 0, row+1
        while i:
            j = col+1
            while j:
                res += self.bit[i][j]
                j -= (j & -j)
            i -= (i & -i)
        return res

    Sigh, java is so much faster

  • 0

    your code is good but just don't put multiple-line assignment in a single line. Such a way makes people really hard to read your code.

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