821. Shortest Distance to a Character

https://leetcode.com/problems/shortest-distance-to-a-character/solution/





// three pass, accepted 
class Solution {
    public int[] shortestToChar(String S, char C) {
        // left scan , update e's index 
        // right scan , update e's index 
        // if no char c found, yet, mark it as interger.max value 
        // final scan, get min, return 
        int n = S.length();
        int[] left = new int[n];
        int[] right = new int[n];
        int charIndex = -1;
        // left scan
        for(int i = 0; i < n; i++){
            if(S.charAt(i) == C){
                charIndex = i;
            }
            if(charIndex < 0){
                left[i] = Integer.MAX_VALUE;
            }else{
                left[i] = i - charIndex;
            } 
        }
        charIndex = -1; // reset
        // right scan
        for(int i = n - 1; i >= 0; i--){
            if(S.charAt(i) == C){
                charIndex = i;
            }
            if(charIndex < 0){
                right[i] = Integer.MAX_VALUE;
            }else{
                right[i] = charIndex - i;
            } 
        }
        // get min
        for(int i = 0; i < n; i++){
            left[i] = Math.min(left[i], right[i]);
        }
        return left;
    }
}





// two pass, accepted 
class Solution {
    public int[] shortestToChar(String S, char C) {
        // left scan , update e's index 
        // right scan , update e's index 
        // if no char c found, yet, mark it as interger.max value 
        // final scan, get min, return 
        int n = S.length();
        int[] left = new int[n];
        int[] right = new int[n];
        int charIndex = -1;
        // left scan
        for(int i = 0; i < n; i++){
            if(S.charAt(i) == C){
                charIndex = i;
            }
            if(charIndex < 0){
                left[i] = Integer.MAX_VALUE;
            }else{
                left[i] = i - charIndex;
            } 
        }
        charIndex = -1; // reset
        // right scan
        for(int i = n - 1; i >= 0; i--){
            if(S.charAt(i) == C){
                charIndex = i;
            }
            if(charIndex < 0){
                right[i] = Integer.MAX_VALUE;
            }else{
                right[i] = charIndex - i;
            } 
            right[i] = Math.min(right[i], left[i]);
        }
 
        return right;
    }
}