solve problem

leet-code/36-valid-sudoku/README.md

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+# 36-valid-sudoku
+
+Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:
+
+1. Each row must contain the digits 1-9 **without repetition**.
+2. Each column must contain the digits 1-9 **without repetition**.
+3. Each of the nine 3 x 3 sub-boxes of the grid must contain the digits 1-9 **without repetition**.
+
+> **Note**:
+>
+> - A Sudoku board (partially filled) could be valid but is not necessarily solvable.
+> - Only the filled cells need to be validated according to the mentioned rules.
+
+### Example 1
+
+**Input:**
+
+```python
+board = [
+  ["5","3",".",".","7",".",".",".","."],
+  ["6",".",".","1","9","5",".",".","."],
+  [".","9","8",".",".",".",".","6","."],
+  ["8",".",".",".","6",".",".",".","3"],
+  ["4",".",".","8",".","3",".",".","1"],
+  ["7",".",".",".","2",".",".",".","6"],
+  [".","6",".",".",".",".","2","8","."],
+  [".",".",".","4","1","9",".",".","5"],
+  [".",".",".",".","8",".",".","7","9"]
+]
+```
+
+**Output:**
+
+```
+true
+```
+
+### Example 2
+
+**Input:**
+
+```python
+board = [
+  ["8","3",".",".","7",".",".",".","."],
+  ["6",".",".","1","9","5",".",".","."],
+  [".","9","8",".",".",".",".","6","."],
+  ["8",".",".",".","6",".",".",".","3"],
+  ["4",".",".","8",".","3",".",".","1"],
+  ["7",".",".",".","2",".",".",".","6"],
+  [".","6",".",".",".",".","2","8","."],
+  [".",".",".","4","1","9",".",".","5"],
+  [".",".",".",".","8",".",".","7","9"]
+]
+```
+
+**Output:**
+
+```
+false
+```
+
+**Explanation:**
+Same as Example 1, except the top left corner is modified to `8`. Since there are two 8's in the top-left 3x3 sub-box, it is invalid.
+
+### Constraints
+
+- `board.length == 9`
+- `board[i].length == 9`
+- `board[i][j]` is a digit `'1'`-`'9'` or `'.'` (empty cell).

leet-code/36-valid-sudoku/index.js

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+/**
+ * @param {character[][]} board
+ * @return {boolean}
+ */
+var isValidSudoku = function(board) {
+    // store which digits have been seen
+    let s = new Set()
+
+    // Check 3x3 grid
+    for (let g = 0; g < 9; g++) {
+        let columnOffset; let rowOffset;
+        // We can use math to compute this but ran out of time
+        if (g === 0) { columnOffset = 0; rowOffset = 0 }
+        if (g === 1) { columnOffset = 3; rowOffset = 0 }
+        if (g === 2) { columnOffset = 6; rowOffset = 0 }
+        if (g === 3) { columnOffset = 0; rowOffset = 3 }
+        if (g === 4) { columnOffset = 3; rowOffset = 3 }
+        if (g === 5) { columnOffset = 6; rowOffset = 3 }
+        if (g === 6) { columnOffset = 0; rowOffset = 6 }
+        if (g === 7) { columnOffset = 3; rowOffset = 6 }
+        if (g === 8) { columnOffset = 6; rowOffset = 6 }
+        for (let i = 0; i < 9; i++) {
+            let colIndex = i % 3
+            let rowIndex = Math.floor(i/3)
+            const element = board[rowIndex + rowOffset][colIndex + columnOffset]
+            if (element === '.') continue
+            // identified rule violation
+            if (s.has(element)) return false 
+            s.add(element)
+        }
+        // reset for each new grid
+        s = new Set()
+    }
+    // reset for next check
+    s = new Set()
+    // Check rows
+    for (let i = 0; i < 9; i++) {
+        const row = board[i]
+        for (let j = 0; j < 9; j++) {
+            const element = row[j]
+            if (element === '.') continue;
+            // identified rule violation
+            if (s.has(element)) return false
+            s.add(element)
+        }
+        // reset for each row
+        s = new Set()
+    }
+
+    s = new Set();
+    // Check columns
+    for (let i = 0; i < 9; i++) {
+        // The ith column in each row
+        for (let j = 0; j < 9; j++) {
+            const element = board[j][i]
+            if (element === '.') continue;
+            // identified rule violation
+            if(s.has(element)) return false;
+            s.add(element)
+        }
+        //reset for each column
+        s = new Set()
+    }
+
+    // never found an invalid case
+    return true;
+};