CF1285D Dr. Evil Underscores

思路：

首先建立字典树，然后递归计算。

实现：

#include<bits/stdc++.h>
using namespace std;

const int INF = 0x7f7f7f7f;
const int N = 100005;
const int MAX_BIT = 31;
int a[N], cnt = 0;

struct trieNode
{
    trieNode* next[2];
};

trieNode pool[N * 32];

trieNode* createTrie()
{
    trieNode* root = &pool[cnt++];
    for (int i = 0; i < 2; i++)
    {
        root->next[i] = NULL;
    }
    return root;
}

void insert(trieNode* root, int x)
{
    trieNode* tmp = root;
    int index;
    for (int i = MAX_BIT; i >= 0; i--)
    {
        int msk = (1 << i);
        if (msk & x) index = 1;
        else index = 0;
        if (tmp->next[index] == NULL)
        {
            tmp->next[index] = createTrie();
        }
        tmp = tmp->next[index];
    }
}

int search(trieNode* root, int d)
{
    if (root->next[0] == NULL and root->next[1] == NULL) return 0;
    if (root->next[0] and root->next[1]) 
    {
        int tmp = min(search(root->next[0], d - 1), search(root->next[1], d - 1));
        return tmp + (1 << d);
    }
    else if (root->next[0]) return search(root->next[0], d - 1);
    else return search(root->next[1], d - 1);
}

int main()
{
    int n;
    while (cin >> n)
    {
        for (int i = 0; i < n; i++) cin >> a[i];
        trieNode* root = createTrie();
        for (int i = 0; i < n; i++) insert(root, a[i]);
        int ans = search(root, 31);
        cout << ans << endl;
    }
    return 0;
}