feat: 剑指 Offer 43. 1～n 整数中 1 出现的次数

剑指offer/I/剑指 Offer 43. 1～n 整数中 1 出现的次数.js

@@ -0,0 +1,27 @@
+/**
+ * @param {number} n
+ * @return {number}
+ */
+const countDigitOne = function (n) {
+  n = `${n}`
+  let i = 0
+  let ans = 0
+  while (i < n.length) {
+    const front = +n.slice(0, i)
+    const end = n.slice(i + 1)
+    const len = end === '' ? 0 : end.length
+
+    let count
+    const cur = +n[i]
+    if (cur > 1)
+      count = (front + 1) * 10 ** len
+    else if (cur === 1)
+      count = front * 10 ** len + (+end) + 1
+    else
+      count = front * 10 ** len
+
+    ans += count
+    i++
+  }
+  return ans
+}