代码随想录算法训练营第25天| 回溯

LeetCode.216 组合总和

def backtrack(res, result, target, start):
    if target <= 0 and len(result) >= k:
        if not target and len(result) == k:
            res.append(list(result))
        return
    for i in range(start, 10):
        result.append(i)
        backtrack(res, result, target-i, i+1)
        result.pop()
res = []
backtrack(res, [], n, 1)
return res

LeetCode.17 电话号码的字母组合

if not digits: return []
phoneMap = {
    "2": "abc",
    "3": "def",
    "4": "ghi",
    "5": "jkl",
    "6": "mno",
    "7": "pqrs",
    "8": "tuv",
    "9": "wxyz",
}
def backtrack(res, result, k):
    if k == len(digits):
        res.append(result)
        return 
    for i in phoneMap[digits[k]]:
        result += i
        backtrack(res, result, k+1)
        result = result[:-1]
res = []
backtrack(res, "", 0)
return res