Solution

Method 1 – Set Exclusion and Minimum Search

Intuition

If a number appears on both sides of the same card, it can never be a good integer (since it will always be facing up on some card). For all other numbers, if it appears on the back of any card and is not excluded, it is a candidate for the answer. The minimum such number is the answer.

Approach

Create a set of numbers that appear on both sides of the same card (excluded set).
For each number on the backs of all cards, if it is not in the excluded set, track the minimum value.
Return the minimum found, or 0 if none exists.

Code

[{"language":"C++","code":"class Solution {\npublic:\n    int flipgame(vector<int>& fronts, vector<int>& backs) {\n        unordered_set<int> same;\n        int n = fronts.size(), ans = INT_MAX;\n        for (int i = 0; i < n; ++i) if (fronts[i] == backs[i]) same.insert(fronts[i]);\n        for (int x : fronts) if (!same.count(x)) ans = min(ans, x);\n        for (int x : backs) if (!same.count(x)) ans = min(ans, x);\n        return ans == INT_MAX ? 0 : ans;\n    }\n};","lang":"cpp","html":"<pre class=\"shiki shiki-themes github-light github-dark\" style=\"background-color:#fff;--shiki-dark-bg:#24292e;color:#24292e;--shiki-dark:#e1e4e8\" tabindex=\"0\"><code><span class=\"line\"><span style=\"color:#D73A49;--shiki-dark:#F97583\">class</span><span style=\"color:#6F42C1;--shiki-dark:#B392F0\"> Solution</span><span style=\"color:#24292E;--shiki-dark:#E1E4E8\"> {</span></span>\n<span class=\"line\"><span style=\"color:#D73A49;--shiki-dark:#F97583\">public:</span></span>\n<span class=\"line\"><span style=\"color:#D73A49;--shiki-dark:#F97583\">    int</span><span style=\"color:#6F42C1;--shiki-dark:#B392F0\"> flipgame</span><span style=\"color:#24292E;--shiki-dark:#E1E4E8\">(</span><span style=\"color:#6F42C1;--shiki-dark:#B392F0\">vector</span><span style=\"color:#24292E;--shiki-dark:#E1E4E8\">&#x3C;</span><span style=\"color:#D73A49;--shiki-dark:#F97583\">int</span><span style=\"color:#24292E;--shiki-dark:#E1E4E8\">></span><span style=\"color:#D73A49;--shiki-dark:#F97583\">&#x26;</span><span style=\"color:#E36209;--shiki-dark:#FFAB70\"> fronts</span><span style=\"color:#24292E;--shiki-dark:#E1E4E8\">, </span><span style=\"color:#6F42C1;--shiki-dark:#B392F0\">vector</span><span style=\"color:#24292E;--shiki-dark:#E1E4E8\">&#x3C;</span><span style=\"color:#D73A49;--shiki-dark:#F97583\">int</span><span style=\"color:#24292E;--shiki-dark:#E1E4E8\">></span><span style=\"color:#D73A49;--shiki-dark:#F97583\">&#x26;</span><span style=\"color:#E36209;--shiki-dark:#FFAB70\"> backs</span><span style=\"color:#24292E;--shiki-dark:#E1E4E8\">) {</span></span>\n<span class=\"line\"><span style=\"color:#24292E;--shiki-dark:#E1E4E8\">        unordered_set</span><span style=\"color:#D73A49;--shiki-dark:#F97583\">&#x3C;int></span><span style=\"color:#24292E;--shiki-dark:#E1E4E8\"> same;</span></span>\n<span class=\"line\"><span style=\"color:#D73A49;--shiki-dark:#F97583\">        int</span><span style=\"color:#24292E;--shiki-dark:#E1E4E8\"> n </span><span style=\"color:#D73A49;--shiki-dark:#F97583\">=</span><span style=\"color:#24292E;--shiki-dark:#E1E4E8\"> fronts.</span><span style=\"color:#6F42C1;--shiki-dark:#B392F0\">size</span><span style=\"color:#24292E;--shiki-dark:#E1E4E8\">(), ans </span><span style=\"color:#D73A49;--shiki-dark:#F97583\">=</span><span style=\"color:#24292E;--shiki-dark:#E1E4E8\"> INT_MAX;</span></span>\n<span class=\"line\"><span style=\"color:#D73A49;--shiki-dark

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