leetcode 953. Verifying an Alien Dictionary & 949. Largest Time for Given Digits & 948. Bag of Tokens

leetcode 953. Verifying an Alien Dictionary

class Solution {
    public boolean isAlienSorted(String[] words, String order) {
        int[] o = new int[26];
        for (int i = 0; i < order.length(); ++i) {
            o[order.charAt(i) - 'a'] = i;
        }
        for (int i = 0; i < words.length - 1;  ++i) {
            if (!inOrder(words[i], words[i + 1], o)) return false;
        }
        return true;
    }
    
    public boolean inOrder(String s1, String s2, int[] order) {
        for (int i = 0; i < s1.length() && i < s2.length(); ++i) {
            int l1 = order[s1.charAt(i) - 'a'];
            int l2 = order[s2.charAt(i) - 'a'];
            if (l1 > l2) return false;
            else if (l1 < l2) return true;
        }
        if (s1.length() > s2.length()) return false;
        else return true;
    }
}

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949. Largest Time for Given Digits

    class Solution {
        public String largestTimeFromDigits(int[] A) {
            String ret = "";
            int time = 0;
            for (int i = 0; i < A.length; ++i) {
                if (A[i] > 2) continue;
                for (int j = 0; j < A.length; ++j) {
                    if (j != i) {
                        if (A[i] == 2 && A[j] > 3) continue;
                        for (int m = 0; m < A.length; ++m) {
                            if (m != i && m != j) {
                                if (A[m] > 5) continue;
                                int idx = 6 - i - j - m;
                                int t = (A[i] * 10 + A[j]) * 60 + (10 * A[m] + A[idx]);
                                if (t >= time) {
                                    time = t;
                                    ret = String.format("%02d:%02d", A[i] * 10 + A[j], 10 *A[m] + A[idx]);
                                }
                            }
                        }
                    }
                }
            }
            return ret;
        }
    }

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948. Bag of Tokens

Greedy solution:

1. Sort tokens first.

2. At each loop, first try to gain as many points as possible from the left of token array. In this way, points are gained with least points possibly.

3. Then exchange power using 1 point from the right of token array. In this way, we can get largest amount of power with 1 point. and continue to step 2 if possible.

    class Solution {
        public int bagOfTokensScore(int[] tokens, int P) {
            Arrays.sort(tokens);
            if (tokens.length == 0 || P < tokens[0]) return 0;
            int l = 0, r = tokens.length - 1;
            int ret = 0;
            int c = 0;
            while (l <= r) {
                while (l <= r && P >= tokens[l]) {
                    c += 1;
                    ret = Math.max(ret, c);
                    P -= tokens[l];
                    l += 1;
                }
                //until cannot trade, gain power with least point and try again in next loop
                if (r >= l && c > 0) {
                    P += tokens[r];
                    r -= 1;
                    c -= 1;
                }
            }
            return ret;
        }
    }