1
class Solution {
2
 public:
3
  vector<int> prevPermOpt1(vector<int> &arr) {
4
    int n = arr.size();
5
    int c1 = n - 2, c2 = n - 1;
6
    while (c1 >= 0 && arr[c1] <= arr[c1 + 1]) c1--;
7
    if (c1 < 0) return arr;
8
    while (arr[c2] >= arr[c1] || c2 > 0 && arr[c2] == arr[c2 - 1]) c2--;
9
    swap(arr[c1], arr[c2]);
10
    return arr;
11
  }
12
};