Create 1643-kth-smallest-instructions.js

Author: everthis

1643-kth-smallest-instructions.js

@@ -0,0 +1,51 @@
+/**
+ * @param {number[]} destination
+ * @param {number} k
+ * @return {string}
+ */
+const kthSmallestPath = function (destination, k) {
+  let v = destination[0],
+    h = destination[1]
+  const mu = (c, n) => {
+    let res = ''
+    for (let i = 0; i < n; i++) {
+      res += c
+    }
+    return res
+  }
+
+  let res = ''
+  while (h > 0 && v > 0) {
+    let pre = comb(h + v - 1, v)
+    if (k <= pre) {
+      res += 'H'
+      h -= 1
+    } else {
+      res += 'V'
+      v -= 1
+      k -= pre
+    }
+  }
+  if (h == 0) res += mu('V', v)
+  if (v == 0) res += mu('H', h)
+  return res
+}
+
+function product(a, b) {
+  let prd = a,
+    i = a
+
+  while (i++ < b) {
+    prd *= i
+  }
+  return prd
+}
+
+function comb(n, r) {
+  if (n == r) {
+    return 1
+  } else {
+    r = r < n - r ? n - r : r
+    return product(r + 1, n) / product(1, n - r)
+  }
+}