Easy Diagonal

easy-diagonal/index.js

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+// https://www.codewars.com/kata/easy-diagonal/train/javascript
+
+function diagonal(n, p) {
+  let rows = (n, fn) => {
+    let l = [1];
+    for (let i = 0; i <= n; ++i) {
+      fn(l);
+      let a = [];
+      for (let j = 0; j <= i+1; ++j) {
+        a[j] = (l[j-1] || 0) + (l[j] || 0);
+      }
+      l = a;
+    }
+  }
+  
+  let sum = 0;
+  rows(n, row => {
+    sum += row[p] || 0;
+  });
+  
+  return sum;
+}