Create 304-range-sum-query-2d-immutable.js

Author: everthis

304-range-sum-query-2d-immutable.js

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+/**
+ * @param {number[][]} matrix
+ */
+const NumMatrix = function(matrix) {
+  const dp = [];
+  if (matrix.length == 0 || matrix[0].length == 0) return;
+  for (let i = 0; i <= matrix.length; i++) {
+    let t = new Array(matrix[0].length + 1).fill(0);
+    dp.push(t);
+  }
+
+  for (let i = 0; i < matrix.length; i++) {
+    for (let j = 0; j < matrix[0].length; j++) {
+      dp[i + 1][j + 1] = dp[i][j + 1] + dp[i + 1][j] + matrix[i][j] - dp[i][j];
+    }
+  }
+
+  this.cache = dp;
+};
+
+/**
+ * @param {number} row1
+ * @param {number} col1
+ * @param {number} row2
+ * @param {number} col2
+ * @return {number}
+ */
+NumMatrix.prototype.sumRegion = function(row1, col1, row2, col2) {
+  const dp = this.cache;
+  return (
+    dp[row2 + 1][col2 + 1] -
+    dp[row1][col2 + 1] -
+    dp[row2 + 1][col1] +
+    dp[row1][col1]
+  );
+};
+
+/**
+ * Your NumMatrix object will be instantiated and called as such:
+ * var obj = Object.create(NumMatrix).createNew(matrix)
+ * var param_1 = obj.sumRegion(row1,col1,row2,col2)
+ */