Update README.md

Author: darusc

README.md

@@ -10,8 +10,58 @@
 
 ## How it works
 
+### Sudoku board detection
 
+To identify the sudoku board the input image is processed as follows with [OpenCV](https://github.com/opencv/opencv):
+- Using the Canny algorithm to detect all contours in the image.
+- The biggest contour corresponds to the whole sudoku puzzle.
+- Use the found contour to extract and warp the sudoku grid .
 
-<img src="demo/demo1.gif" width=100%></img>
+The numbers are detected using [MLKit Text Recognition](https://developers.google.com/ml-kit/vision/text-recognition/v2).
+
+<br>
+
+<p align="center">
+  <img src="demo/demo1.gif"></img>
+</p>
+
+<br>
+
+### Solving
+For solving the puzzle I'm using a fairly simple, brute-force algorithm that relies on backtracking to generate the valid solution. 
+<br>
+It goes through the whole 2D array and for each number that needs to be found it tries all possibilities and continues with the following numbers. 
+<br> 
+<br>
+For each cell there are 9 possible numbers which means the time complexity of this algorithm is O(9<sup>N</sup>).
+
+```
+private fun solve(index: Int = 0): Boolean {
+    for (i in index until 81) {
+        val r = i / 9
+        val c = i % 9
+        if (sudokuBoard[r][c].number == 0) {
+            for (n in 1..9) {
+                if (isValidSolution(r, c, n)) {
+                    sudokuBoard[r][c].number = n
+                    if (solve(i + 1)) {
+                        return true
+                    }
+                    sudokuBoard[r][c].number = 0
+                }
+            }
+            return false
+        }
+    }
+    return true
+}
+```
+<br>
+<p align="center">
+  <img src="demo/demo2.gif"></img>
+</p>
+<p align="center">
+  <span>Solve algorithm demo</span>
+</p>
 
 ## Getting Started