Create 402-remove-k-digits.js

Author: everthis

402-remove-k-digits.js

@@ -0,0 +1,26 @@
+/**
+ * @param {string} num
+ * @param {number} k
+ * @return {string}
+ */
+const removeKdigits = function(num, k) {
+  const digits = num.length - k;
+  const stk = new Array(num.length);
+  let top = 0;
+  // k keeps track of how many characters we can remove
+  // if the previous character in stk is larger than the current one
+  // then removing it will get a smaller number
+  // but we can only do so when k is larger than 0
+  for (let i = 0; i < num.length; i++) {
+    let c = num.charAt(i);
+    while (top > 0 && stk[top - 1] > c && k > 0) {
+      top -= 1;
+      k -= 1;
+    }
+    stk[top++] = c;
+  }
+  // find the index of first non-zero digit
+  let idx = 0;
+  while (idx < digits && stk[idx] === "0") idx++;
+  return idx === digits ? "0" : stk.slice(idx, digits + idx).join("");
+};