[LeetCode] Shortest Distance to a Character

Problem

Given a string S and a character C, return an array of integers representing the shortest distance from the character C in the string.

Example 1:

Input: S = "loveleetcode", C = 'e'
Output: [3, 2, 1, 0, 1, 0, 0, 1, 2, 2, 1, 0]

Note:

S string length is in [1, 10000].
C is a single character, and guaranteed to be in string S.
All letters in S and C are lowercase.

Solution

class Solution {
    public int[] shortestToChar(String S, char C) {
        int len = S.length();
        int[] res = new int[len];
        if (S == null || S.length() == 0) return res;
        Arrays.fill(res, 10000);
        int pre = -1;
        for (int i = 0; i < len; i++) {
            char ch = S.charAt(i);
            if (ch == C) {
                pre = i;
                res[i] = 0;
            } else {
                if (pre != -1) {
                    res[i] = i-pre;
                }
            }
        }
        pre = -1;
        for (int i = len-1; i >= 0; i--) {
            char ch = S.charAt(i);
            if (ch == C) {
                pre = i;
            } else {
                if (pre != -1) {
                    res[i] = Math.min(res[i], pre-i);
                }
            }
        }
        return res;
    }
}