Create 2030-smallest-k-length-subsequence-with-occurrences-of-a-letter.js

Author: everthis

2030-smallest-k-length-subsequence-with-occurrences-of-a-letter.js

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+/**
+ * @param {string} s
+ * @param {number} k
+ * @param {character} letter
+ * @param {number} repetition
+ * @return {string}
+ */
+const smallestSubsequence = function (s, k, letter, repetition) {
+  let n_letters = 0
+  for (let i = 0; i < s.length; i++) if (s.charAt(i) == letter) n_letters++
+  const stack = []
+  for (let i = 0; i < s.length; i++) {
+    let c = s.charAt(i)
+    while (
+      stack.length &&
+      stack[stack.length - 1] > c &&
+      s.length - i + stack.length > k &&
+      (stack[stack.length - 1] != letter || n_letters > repetition)
+    ) {
+      if (stack.pop() == letter) repetition++
+    }
+    if (stack.length < k) {
+      if (c == letter) {
+        stack.push(c)
+        repetition--
+      } else if (k - stack.length > repetition) {
+        stack.push(c)
+      }
+    }
+    if (c == letter) n_letters--
+  }
+
+  let sb = ''
+  for (let c of stack) sb += c
+  return sb
+}