Sep4: Sort, permutation [M]

basic logic and sort problem, O(NlogN), O(1)

daily/Sep4.cc

@@ -0,0 +1,21 @@
+#include <iostream>
+#include <vector>
+using namespace std;
+
+class Solution {
+ public:
+  /**
+   * @brief LC2860: happy students [M]
+   * Permutation, sort, Time: O(NlogN), Space: O(1)
+   *
+   * @param nums
+   * @return int
+   */
+  int countWays(vector<int>& nums) {
+    int ans = nums[0] > 0;  // non selected
+    for (int i = 1; i < nums.size(); i++) {
+      ans += nums[i - 1] < i && i < nums[i];
+    }
+    return ans + 1;  // all selected
+  }
+};