Add solution #1314

Author: JoshCrozier

README.md

@@ -1,4 +1,4 @@
-# 1,226 LeetCode solutions in JavaScript
+# 1,227 LeetCode solutions in JavaScript
 
 [https://leetcodejavascript.com](https://leetcodejavascript.com)
 
@@ -995,6 +995,7 @@
 1311|[Get Watched Videos by Your Friends](./solutions/1311-get-watched-videos-by-your-friends.js)|Medium|
 1312|[Minimum Insertion Steps to Make a String Palindrome](./solutions/1312-minimum-insertion-steps-to-make-a-string-palindrome.js)|Hard|
 1313|[Decompress Run-Length Encoded List](./solutions/1313-decompress-run-length-encoded-list.js)|Easy|
+1314|[Matrix Block Sum](./solutions/1314-matrix-block-sum.js)|Medium|
 1317|[Convert Integer to the Sum of Two No-Zero Integers](./solutions/1317-convert-integer-to-the-sum-of-two-no-zero-integers.js)|Easy|
 1318|[Minimum Flips to Make a OR b Equal to c](./solutions/1318-minimum-flips-to-make-a-or-b-equal-to-c.js)|Medium|
 1319|[Number of Operations to Make Network Connected](./solutions/1319-number-of-operations-to-make-network-connected.js)|Medium|

solutions/1314-matrix-block-sum.js

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+/**
+ * 1314. Matrix Block Sum
+ * https://leetcode.com/problems/matrix-block-sum/
+ * Difficulty: Medium
+ *
+ * Given a m x n matrix mat and an integer k, return a matrix answer where each answer[i][j]
+ * is the sum of all elements mat[r][c] for:
+ * - i - k <= r <= i + k,
+ * - j - k <= c <= j + k, and
+ * - (r, c) is a valid position in the matrix.
+ */
+
+/**
+ * @param {number[][]} mat
+ * @param {number} k
+ * @return {number[][]}
+ */
+var matrixBlockSum = function(mat, k) {
+  const rows = mat.length;
+  const cols = mat[0].length;
+  const prefixSums = new Array(rows + 1).fill().map(() => new Array(cols + 1).fill(0));
+
+  for (let i = 0; i < rows; i++) {
+    for (let j = 0; j < cols; j++) {
+      prefixSums[i + 1][j + 1] = prefixSums[i + 1][j]
+        + prefixSums[i][j + 1] - prefixSums[i][j] + mat[i][j];
+    }
+  }
+
+  const result = new Array(rows).fill().map(() => new Array(cols).fill(0));
+
+  for (let i = 0; i < rows; i++) {
+    for (let j = 0; j < cols; j++) {
+      const top = Math.max(0, i - k);
+      const bottom = Math.min(rows - 1, i + k);
+      const left = Math.max(0, j - k);
+      const right = Math.min(cols - 1, j + k);
+
+      result[i][j] = prefixSums[bottom + 1][right + 1]
+        - prefixSums[bottom + 1][left] - prefixSums[top][right + 1] + prefixSums[top][left];
+    }
+  }
+
+  return result;
+};