Cat Sudoku Level 21 Hint
Find a colored region with only a few safe cells, then compare those cells against the row and column limits.
Cat Sudoku Level 21 Strategy
Easy Level 21 uses a 7x7 board with 7 colored regions. It starts with 2 fixed cats to anchor the solve. Work from the tightest rows and regions before placing a cat.
Cat Sudoku Level 21 Solution
Solution cells: R1C5, R2C2, R3C6, R4C3, R5C7, R6C4, R7C1.