feat: add js solution to lc problem: No.0840

Author: rain84

solution/0800-0899/0840.Magic Squares In Grid/README.md

@@ -318,6 +318,56 @@ function numMagicSquaresInside(grid: number[][]): number {
 }
 ```
 
+#### JavaScript
+
+```js
+function numMagicSquaresInside(grid) {
+    const m = grid.length;
+    const n = grid[0].length;
+    const check = (i, j) => {
+        if (i + 3 > m || j + 3 > n) {
+            return 0;
+        }
+        const cnt = Array(16).fill(0);
+        const row = Array(3).fill(0);
+        const col = Array(3).fill(0);
+        let [a, b] = [0, 0];
+        for (let x = i; x < i + 3; ++x) {
+            for (let y = j; y < j + 3; ++y) {
+                const v = grid[x][y];
+                if (v < 1 || v > 9 || ++cnt[v] > 1) {
+                    return 0;
+                }
+                row[x - i] += v;
+                col[y - j] += v;
+                if (x - i === y - j) {
+                    a += v;
+                }
+                if (x - i === 2 - (y - j)) {
+                    b += v;
+                }
+            }
+        }
+        if (a !== b) {
+            return 0;
+        }
+        for (let k = 0; k < 3; ++k) {
+            if (row[k] !== a || col[k] !== a) {
+                return 0;
+            }
+        }
+        return 1;
+    };
+    let ans = 0;
+    for (let i = 0; i < m; ++i) {
+        for (let j = 0; j < n; ++j) {
+            ans += check(i, j);
+        }
+    }
+    return ans;
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

solution/0800-0899/0840.Magic Squares In Grid/README_EN.md

@@ -314,6 +314,56 @@ function numMagicSquaresInside(grid: number[][]): number {
 }
 ```
 
+#### JavaScript
+
+```js
+function numMagicSquaresInside(grid) {
+    const m = grid.length;
+    const n = grid[0].length;
+    const check = (i, j) => {
+        if (i + 3 > m || j + 3 > n) {
+            return 0;
+        }
+        const cnt = Array(16).fill(0);
+        const row = Array(3).fill(0);
+        const col = Array(3).fill(0);
+        let [a, b] = [0, 0];
+        for (let x = i; x < i + 3; ++x) {
+            for (let y = j; y < j + 3; ++y) {
+                const v = grid[x][y];
+                if (v < 1 || v > 9 || ++cnt[v] > 1) {
+                    return 0;
+                }
+                row[x - i] += v;
+                col[y - j] += v;
+                if (x - i === y - j) {
+                    a += v;
+                }
+                if (x - i === 2 - (y - j)) {
+                    b += v;
+                }
+            }
+        }
+        if (a !== b) {
+            return 0;
+        }
+        for (let k = 0; k < 3; ++k) {
+            if (row[k] !== a || col[k] !== a) {
+                return 0;
+            }
+        }
+        return 1;
+    };
+    let ans = 0;
+    for (let i = 0; i < m; ++i) {
+        for (let j = 0; j < n; ++j) {
+            ans += check(i, j);
+        }
+    }
+    return ans;
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

solution/0800-0899/0840.Magic Squares In Grid/Solution.js

@@ -0,0 +1,45 @@
+function numMagicSquaresInside(grid) {
+    const m = grid.length;
+    const n = grid[0].length;
+    const check = (i, j) => {
+        if (i + 3 > m || j + 3 > n) {
+            return 0;
+        }
+        const cnt = Array(16).fill(0);
+        const row = Array(3).fill(0);
+        const col = Array(3).fill(0);
+        let [a, b] = [0, 0];
+        for (let x = i; x < i + 3; ++x) {
+            for (let y = j; y < j + 3; ++y) {
+                const v = grid[x][y];
+                if (v < 1 || v > 9 || ++cnt[v] > 1) {
+                    return 0;
+                }
+                row[x - i] += v;
+                col[y - j] += v;
+                if (x - i === y - j) {
+                    a += v;
+                }
+                if (x - i === 2 - (y - j)) {
+                    b += v;
+                }
+            }
+        }
+        if (a !== b) {
+            return 0;
+        }
+        for (let k = 0; k < 3; ++k) {
+            if (row[k] !== a || col[k] !== a) {
+                return 0;
+            }
+        }
+        return 1;
+    };
+    let ans = 0;
+    for (let i = 0; i < m; ++i) {
+        for (let j = 0; j < n; ++j) {
+            ans += check(i, j);
+        }
+    }
+    return ans;
+}