1405

1405. Longest Happy String (Medium)

A string is called happy if it does not have any of the strings 'aaa', 'bbb' or 'ccc' as a substring.

Given three integers a, b and c, return any string s, which satisfies following conditions:

• s is happy and longest possible.
• s contains at most a occurrences of the letter 'a', at most b occurrences of the letter 'b' and at most c occurrences of the letter 'c'.
• s will only contain 'a', 'b' and 'c' letters.

If there is no such string s return the empty string "".

 

Example 1:

Input: a = 1, b = 1, c = 7
Output: "ccaccbcc"
Explanation: "ccbccacc" would also be a correct answer.

Example 2:

Input: a = 2, b = 2, c = 1
Output: "aabbc"

Example 3:

Input: a = 7, b = 1, c = 0
Output: "aabaa"
Explanation: It's the only correct answer in this case.

 

Constraints:

• 0 <= a, b, c <= 100
• a + b + c > 0

Related Topics:
Dynamic Programming, Greedy

Solution 1.

// OJ: https://leetcode.com/problems/longest-happy-string/
// Author: github.com/lzl124631x
// Time: O(A+B+C)
// Space: O(1)
class Solution {
public:
    string longestDiverseString(int a, int b, int c) {
        int cnt[3] = {a, b, c}, prev = -1;
        string ans;
        while (true) {
            int maxIndex = -1;
            for (int i = 0; i < 3; ++i) {
                if (i != prev && (maxIndex == -1 || cnt[i] > cnt[maxIndex])) maxIndex = i;
            }
            if (cnt[maxIndex] == 0) break;
            int num = min(2, cnt[maxIndex]);
            if (prev != -1 && cnt[prev] > cnt[maxIndex]) num = 1;
            cnt[maxIndex] -= num;
            while (num--) ans.push_back(maxIndex + 'a');
            prev = maxIndex;
        }
        return ans;
    }
};