Create 668-kth-smallest-number-in-multiplication-table.js

Author: everthis

668-kth-smallest-number-in-multiplication-table.js

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+/**
+ * @param {number} m
+ * @param {number} n
+ * @param {number} k
+ * @return {number}
+ */
+const findKthNumber = function(m, n, k) {
+  let left = 1;
+  let right = m * n;
+  while (left < right) {
+    const mid = Math.floor((left + right) / 2);
+    const nSmaller = count(m, n, mid);
+    if (nSmaller >= k) {
+      right = mid;
+    } else {
+      left = mid + 1;
+    }
+  }
+  return left;
+};
+
+function count(m, n, target) {
+  let nSmaller = 0;
+  let j = n;
+  for (let i = 1; i <= m; i++) {
+    while (i * j > target) {
+      j -= 1;
+    }
+    nSmaller += j;
+  }
+  return nSmaller;
+}