Leetcode 1252. Cells with Odd Values in a Matrix

Given an m×n zero matrix and a list of indices where each (r,c) increments all cells in row r and column c, determine how many cells are odd after all operations. Key idea: track parity of row/column increments (O(m+n+indices.length) time, O(m+n) space); number of odd cells = odd_rows*(n-odd_cols) + (m-odd_rows)*odd_cols.