By now, you are given a secret signature consisting of character 'D' and 'I'. 'D' represents a decreasing relationship between two numbers, 'I' represents an increasing relationship between two numbers. And our secret signature was constructed by a special integer array, which contains uniquely all the different number from 1 to n (n is the length of the secret signature plus 1). For example, the secret signature "DI" can be constructed by array [2,1,3] or [3,1,2], but won't be constructed by array [3,2,4] or [2,1,3,4], which are both illegal constructing special string that can't represent the "DI" secret signature. On the other hand, now your job is to find the lexicographically smallest permutation of [1, 2, ... n] could refer to the given secret signature in the input.
public class Solution {
public int[] findPermutation(String s) {
int[] res = new int[s.length() + 1];
Stack < Integer > stack = new Stack < > ();
int j = 0;
for (int i = 1; i <= s.length(); i++) {
if (s.charAt(i - 1) == 'I') {
stack.push(i);
while (!stack.isEmpty())
res[j++] = stack.pop();
} else
stack.push(i);
}
stack.push(s.length() + 1);
while (!stack.isEmpty())
res[j++] = stack.pop();
return res;
}
}