Leetcode 942. DI String Match

Given a string s of 'I' and 'D' of length n, construct any permutation of [0..n] such that perm[i] < perm[i+1] when s[i]=='I' and perm[i] > perm[i+1] when s[i]=='D'. This is solved greedily by assigning the smallest or largest remaining numbers to satisfy each local inequality.