Find the next lexicographically smaller permutation of the input. For example, the next smaller permutation of “4312” is “4231”. Below are steps to find the previous permutation: Find largest index i such that str[i – 1] > str[i]. Find largest index j such that j >= i and str[j] < str[i – 1]. Swap str[j] and str[i – 1]. Reverse the sub-array starting at str[i].