7020. 统计对称整数的数目 - 力扣（LeetCode）

思路：转化为字符串后枚举

class Solution {
public:int countSymmetricIntegers(int low, int high) {int res = 0;for(int i = low; i <= high; i ++ ){string s = to_string(i);if(s.size() % 2) continue;int pre = 0, suf = 0;for(int i = 0; i < s.size() / 2; i ++ ) pre += s[i] - 'a';for(int i = s.size() / 2; i < s.size(); i ++ ) suf += s[i] - 'a';res += (pre == suf);}return res;}
};

8040. 生成特殊数字的最少操作 - 力扣（LeetCode）

思路：枚举，rfind()

class Solution {
public:int minimumOperations(string num) {int n = num.size();auto f = [&](string tail) {int i = num.rfind(tail[1]);if(i == string::npos || i == 0) return n;i = num.rfind(tail[0], i - 1);if(i == string::npos) return n;return n - i - 2;};return min({n - (num.find('0') != string::npos), f("00"), f("25"), f("50"), f("75")});}
};