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tutorials/summed_area/snippets/countSquares.js

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+// where tl and br are the top left and bottom right cell respectively
+function countSquares(tl, br) {
+
+    // these are the four cells to interrogate
+    let topLeft, left, top, whole;
+
+    // 1d index = x + #rows * y
+    topLeft = t[(tl.x - 1) + n * (tl.y - 1)].count;
+    left = t[(tl.x - 1) + n * bry].count;
+    top = t[br.x + n * (tl.y - 1)].count;
+    whole = t[br.x + n * br.y].count;
+
+    return whole + topLeft - top - left;
+}