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+<html>
+
+<!-- 
+    Task 2 from
+    https://perlweeklychallenge.org/blog/perl-weekly-challenge-077/
+    
+    Comments: https://andrewshitov.com/2020/09/08/lonely-x-the-weekly-challenge-77-task-2/
+-->
+    
+<head>
+    <meta charset="UTF-8"/>
+    <title>Lonely X</title>
+    <style>
+        * {
+            text-align: center;
+            font-family: Arial, sans-serif;
+        }
+        #Shape table {
+            margin: auto;
+            /* border-collapse: collapse; */
+        }
+        #Shape table tr td input {
+            width: 50px;
+            height: 50px;
+        }
+        #Shape table tr td {
+            border: 5px solid white;
+            
+        }
+        #Shape table tr td.lonely {
+            border: 5px solid green;
+        }
+    </style>
+</head>
+<body>
+    <p>
+        <input type="text" name="width" id="MatrixWidth" size="3" value="3" />
+        ×        
+        <input type="text" name="height" id="MatrixHeight" size="3" value="3" />
+        &nbsp;
+        <input type="submit" value="Set the shape" onclick="set_shape()" />
+    </p>
+
+    <div id="Shape"></div>
+
+    <p>Note: Lonely X is marked green.</p>
+
+    <script>
+        let w = 0;
+        let h = 0;
+
+        function set_shape() {
+            w = parseInt(document.getElementById('MatrixWidth').value);
+            h = parseInt(document.getElementById('MatrixHeight').value);
+            
+            let table = '<table>';
+            for (let y = 0; y != h; y++) {
+                table += '<tr>';
+                for (let x = 0; x != w; x++) {
+                    table += '<td><input type="checkbox" data-x="' + x + '" data-y="' + y + '" onclick="update_lonely()" /></td>';
+                }
+                table += '</tr>';
+            }
+            table += '</table>';
+            document.getElementById('Shape').innerHTML = table;
+        }
+
+        function update_lonely() {
+            let cells = document.getElementById('Shape').getElementsByTagName('input');
+            
+            let neigbours = [[0, 1], [0, -1], [1, 0], [-1, 0], [1, 1], [-1, -1], [1, -1], [-1, 1]];
+
+            for (let i = 0; i != cells.length; i++) {
+                cells[i].parentNode.className = '';
+
+                if (!cells[i].checked) continue;
+                let x = parseInt(cells[i].getAttribute('data-x'));
+                let y = parseInt(cells[i].getAttribute('data-y'));
+
+                let is_ok = true;
+                for (let c = 0; c != neigbours.length; c++) {
+                    if (!test_cell(x + neigbours[c][0], y + neigbours[c][1])) {
+                        is_ok = false;
+                        break;
+                    }
+                }
+
+                if (is_ok) {
+                    cells[i].parentNode.className = 'lonely';
+                }
+            }
+        }
+
+        function test_cell(x, y) {
+            if (x < 0 || y < 0 || x >= w || y >= h) {
+                return true;
+            }
+            else {
+                let cell = document.querySelector('#Shape tr td input[data-x="'+ x + '"][data-y="' + y + '"]');
+                return !cell.checked;
+            }
+        }
+
+        set_shape();
+    </script>
+</body>
+</html>