Leetcode – Range Addition II Solution in Python

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In the fascinating world of matrix manipulation, there is a plethora of intriguing problems that test a variety of skills. One such problem is the Range Addition II, listed as problem #598 on LeetCode. This problem serves as an excellent introduction to optimizing matrix operations. In this article, we will meticulously break down the problem, explore different approaches, and learn how to implement an efficient solution in Python.

Problem Statement

Let’s first understand what the problem is asking. The Range Addition II problem statement is as follows:

You are given an m x n matrix M initialized with all 0‘s and an array of operations ops, where ops[i] = [ai, bi] means M[x][y] should be incremented by one for all 0 <= x < ai and 0 <= y < bi.

Count and return the number of maximum integers in the matrix after performing all the operations.


Input: m = 3, n = 3, ops = [[2,2],[3,3]]
Output: 4
Initially, M = [[0, 0, 0], [0, 0, 0], [0, 0, 0]]

After performing [2,2], M = [[1, 1, 0], [1, 1, 0], [0, 0, 0]]

After performing [3,3], M = [[2, 2, 1], [2, 2, 1], [1, 1, 1]]

The maximum integer in M is 2, and there are four of it in M. So return 4.

Intuitive Approach: Brute Force

An intuitive way to solve this problem is to simulate the operations on the matrix and then count the maximum integers. However, this method is not efficient and will not scale well for large inputs.

def maxCount(m, n, ops):
    # Initialize the matrix with zeros
    matrix = [[0] * n for _ in range(m)]
    # Perform the operations
    for op in ops:
        for i in range(op[0]):
            for j in range(op[1]):
                matrix[i][j] += 1
    # Find the maximum integer in the matrix
    max_int = max(max(row) for row in matrix)
    # Count the number of maximum integers
    return sum(row.count(max_int) for row in matrix)

This approach has a time complexity of O(m * n * k), where m and n are the dimensions of the matrix and k is the number of operations. This is highly inefficient for large values of m, n, or k.

Optimized Approach: Analyzing Patterns

The brute force approach is inefficient because it performs unnecessary calculations. If we observe carefully, the maximum integer will always be in the top-left rectangle of size (minimum a_i, minimum b_i), where a_i and b_i are the elements of the ops array.

We can improve the algorithm by finding the dimensions of this rectangle and simply multiplying them together to find the number of maximum integers.

def maxCount(m, n, ops):
    # Find the dimensions of the top-left rectangle
    min_a = m
    min_b = n
    for op in ops:
        min_a = min(min_a, op[0])
        min_b = min(min_b, op[1])
    # The number of maximum integers is the area of the top-left rectangle
    return min_a * min_b

This optimized approach has a time complexity of O(k), where k is the number of operations, and a space complexity of O(1).


The Range Addition II problem serves as an example of how seemingly complex matrix manipulation can be optimized by carefully analyzing the problem’s structure and patterns. Instead of directly simulating each operation, we reduced the problem to finding the dimensions of a specific rectangle in the matrix. This not only made the solution more elegant but also significantly more efficient.

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