From 85cb4aa36b7ba3f49fdd038810cca20fde8b6d23 Mon Sep 17 00:00:00 2001
From: Lars Bonczek <lars.bonczek@gmail.com>
Date: Sun, 2 Nov 2025 13:42:02 +0100
Subject: [PATCH 1/2] Implement puzzle uniqueness

---
 sudoku.js | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/sudoku.js b/sudoku.js
index 65039da..54d2819 100644
--- a/sudoku.js
+++ b/sudoku.js
@@ -80,11 +80,9 @@
         e.g., 0 -> 17, and 100 -> 81.
         
         
-        By default, the puzzles are unique, uless you set `unique` to false. 
+        By default, the puzzles are unique, unless you set `unique` to false. 
         (Note: Puzzle uniqueness is not yet implemented, so puzzles are *not* 
         guaranteed to have unique solutions)
-        
-        TODO: Implement puzzle uniqueness
         */
         
         // If `difficulty` is a string or undefined, convert it to a number or
@@ -98,7 +96,9 @@
                 MIN_GIVENS);
         
         // Default unique to true
-        unique = unique || true;
+        if(typeof unique === "undefined"){
+            unique = true;
+        }
         
         // Get a set of squares and all possible candidates for each square
         var blank_board = "";
@@ -161,8 +161,17 @@
                 
                 // Double check board is solvable
                 // TODO: Make a standalone board checker. Solve is expensive.
-                if(sudoku.solve(board)){
-                    return board;
+                const solution = sudoku.solve(board);
+                if(solution){
+                    if(!unique){
+                        return board;
+                    }
+                    // Check if "backwards" solution is equal to regular solution.
+                    // If it is, the sudoku has a unique solution.
+                    const reverseSolution = sudoku.solve(board, true);
+                    if(reverseSolution == solution){
+                        return board;
+                    }
                 }
             }
         }

From abe627c09aa62f42abab088c39c1856acdd8c80b Mon Sep 17 00:00:00 2001
From: Lars Bonczek <lars.bonczek@gmail.com>
Date: Sun, 2 Nov 2025 13:58:52 +0100
Subject: [PATCH 2/2] Update README.md

---
 README.md | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/README.md b/README.md
index ef28ce7..71c7bcc 100644
--- a/README.md
+++ b/README.md
@@ -83,9 +83,6 @@ false, e.g.,
 sudoku.generate("easy", false)
 ```
 
-Note: **Puzzle uniqueness is not yet implemented**, so puzzles are *not* 
-guaranteed to have unique solutions.
-
 
 Solve a Sudoku puzzle
 --------------------------------------------------------------------------------