Replacing Val

Problem Overview

• Replace the value at a given start cell in a 2D int array and all side-connected cells that share the original value with a new value.
• Input: matrix, start position (row, col), replacement value; Output: updated matrix; constraints unspecified.
• Context: region filling in grid-based data like images or maps.
• From Two_sigma interviews; a classic coding interview problem and common interview question on handling grid updates.