for-each not applicable to expression type

  • 0
    public class Solution {
        public List<String> letterCombinations(String digits) {
            List<String> res = new LinkedList<>();
            if(digits == null || digits.length() == 0){ 
                return res;
            HashMap map = new HashMap();
            map.put('0', new char[] {'0'});
            map.put('1', new char[] {'1'});
            map.put('2', new char[] {'a','b','c'});
            map.put('3', new char[] {'d','e','f'});
            map.put('4', new char[] {'g','h','i'});
            map.put('5', new char[] {'j','k','l'});
            map.put('6', new char[] {'m','n','o'});
            map.put('7', new char[] {'p','q','r','s'});
            map.put('8', new char[] {'t','u','v'});
            map.put('9', new char[] {'w','x','y','z'});
            backtrack(res, map, digits, new StringBuilder());
            return res;
        public void backtrack (List<String> res, HashMap map, String ca, StringBuilder sb){
            if (sb.length() == ca.length()){
                    for (char c : map.get(ca.charAt(0))){
                        backtrack(res, map, ca.substring(1,ca.length(), sb));

    so I have this "for-each not applicable to expression type" error when trying to run my code on line 31, which is

    for (char c : map.get(ca.charAt(0))){

    map should get the corresponding char array and I am pretty sure for each should work with array. Then why is this wrong?


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