feat: 字母迭代组合器

Author: sl1673495

递归与回溯/字母迭代组合器-1286.js

@@ -0,0 +1,52 @@
+/**
+ * @param {string} characters
+ * @param {number} combinationLength
+ */
+let CombinationIterator = function (characters, combinationLength) {
+  let cl = characters.length
+  let res = []
+  let helper = (start, prev) => {
+    let pl = prev.length
+    for (let i = start; i < cl; i++) {
+      let rest = cl - i
+      let diff = combinationLength - pl
+      if (diff > rest) {
+        return
+      }
+      let next = prev + characters[i]
+      if (next.length == combinationLength) {
+        res.push(next)
+      } else {
+        helper(i + 1, next)
+      }
+    }
+  }
+  helper(0, "")
+  this.res = res.sort((a, b) => (a > b ? 1 : -1))
+  this.point = 0
+}
+
+/**
+ * @return {string}
+ */
+CombinationIterator.prototype.next = function () {
+  if (!this.hasNext()) {
+    return undefined
+  }
+  let val = this.res[this.point++]
+  return val
+}
+
+/**
+ * @return {boolean}
+ */
+CombinationIterator.prototype.hasNext = function () {
+  return this.point !== this.res.length
+}
+
+/**
+ * Your CombinationIterator object will be instantiated and called as such:
+ * var obj = new CombinationIterator(characters, combinationLength)
+ * var param_1 = obj.next()
+ * var param_2 = obj.hasNext()
+ */