leetcode1405

第一种方案，使用堆：

from heapq import heappush, heappop
class Solution:
    def longestDiverseString(self, a: int, b: int, c: int) -> str:
        max_heap = []
        if a != 0:
            heappush(max_heap, (-a, 'a'))
        if b != 0:
            heappush(max_heap, (-b, 'b'))
        if c != 0:
            heappush(max_heap, (-c, 'c'))
        s = []
        while max_heap:
            first, char1 = heappop(max_heap) # char with most rest numbers
            if len(s) >= 2 and s[-1] == s[-2] == char1: # check whether this char is the same with previous two
                if not max_heap: # if there is no other choice, just return
                    return ''.join(s)
                second, char2 = heappop(max_heap) # char with second most rest numbers
                s.append(char2)
                second += 1 # count minus one, because the second here is negative, thus add 1
                if second != 0: # only if there is rest number count, add it back to heap
                    heappush(max_heap, (second, char2))
                heappush(max_heap, (first, char1)) # also need to put this part back to heap
                continue
            
            #  situation that this char can be directly added to answer
            s.append(char1)
            first += 1
            if first != 0:
                heappush(max_heap, (first, char1))
        return ''.join(s)
        

参考：https://leetcode.com/problems/longest-happy-string/discuss/564248/Python-HEAP-solution-with-explanation

第二种方案，使用递归：

class Solution(object):
    def longestDiverseString(self, a, b, c, a_chr="a", b_chr="b", c_chr="c"):
        if not (a <= b <= c):
            data = sorted([(a, a_chr), (b, b_chr), (c, c_chr)])
            return self.longestDiverseString(data[0][0], data[1][0], data[2][0], data[0][1], data[1][1], data[2][1])
        if b == 0:
            return c_chr * min(2, c)
        if b == c:
            return c_chr + b_chr + self.longestDiverseString(a, b - 1, c - 1, a_chr, b_chr, c_chr)
        return c_chr * 2 + b_chr + self.longestDiverseString(a, b - 1, c - 2, a_chr, b_chr, c_chr)

参考：https://leetcode.com/problems/longest-happy-string/discuss/565488/Python-Simple-Recursion