2437. 有效时间的数目

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Java：回溯

class Solution {int res = 0;public int countTime(String time) {char[] arr = time.toCharArray();dfs(arr, 0);return res;}public void dfs(char[] arr, int pos) {if (pos == arr.length) {if (check(arr)) {res++;}return;}if (arr[pos] == '?') {for (int i = 0; i <= 9; i++) {arr[pos] = (char) ('0' + i);dfs(arr, pos + 1);arr[pos] = '?';}} else {dfs(arr, pos + 1);}}public boolean check(char[] arr) {int hh = (arr[0] - '0') * 10 + arr[1] - '0';int mm = (arr[3] - '0') * 10 + arr[4] - '0';return hh < 24 && mm < 60;}
}