add: 寻找重复数

src/array/find-the-duplicate-number.js

@@ -0,0 +1,24 @@
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+export const findDuplicate = function (nums) {
+  const len = nums.length
+  let l = 0; let r = len - 1; let res = -1 // 数字都在1-n
+  while (l <= r) {
+    const mid = (l + r) >> 1
+    let cnt = 0
+    for (let i = 0; i < len; i++) {
+      cnt += nums[i] <= mid // true = 1，满足条件才计数
+    }
+
+    if (cnt <= mid) {
+      l = mid + 1
+    } else {
+      r = mid - 1
+      res = mid
+    }
+  }
+
+  return res
+}