3644. Maximum K to Sort a Permutation

You are given an integer array nums of length n, where nums is a permutation of the numbers in the range [0..n - 1].

You may swap elements at indices i and j only if nums[i] AND nums[j] == k, where AND denotes the bitwise AND operation and k is a non-negative integer.

Return the maximum value of k such that the array can be sorted in non-decreasing order using any number of such swaps. If nums is already sorted, return 0.

class Solution {
public:
    int sortPermutation(vector<int>& nums) {
        int res = INT_MAX, n = nums.size();
        for(int i = 0; i < n; i++) {
            if(nums[i] != i) {
                res &= i;
            }
        }
        return res == INT_MAX ? 0 : res;
    }
};