#include <iostream>
#include <vector>
#include <unordered_set>
#include <algorithm>
using namespace std;

const int MAXN = 100005;
int a[MAXN];
int first[MAXN]; // 存储每个数字首次出现的索引
int last[MAXN];  // 存储每个数字最后一次出现的索引
unordered_set<int> elements; // 存储当前区间内出现过的元素

int main() {
    int n, q;
    cin >> n >> q;
    for (int i = 1; i <= n; ++i) {
        cin >> a[i];
        first[a[i]] = i;
        last[a[i]] = i;
    }

    while (q--) {
        int l, r;
        cin >> l >> r;
        elements.clear();
        int maxR = 0, minL = r + 1;
        for (int i = l; i <= r; ++i) {
            elements.insert(a[i]);
            last[a[i]] = i;
        }

        for (int num : elements) {
            int curL = first[num];
            int curR = last[num];
            if (curL > maxR) maxR = curL;
            if (curR < minL) minL = curR;
        }

        cout << minL - maxR + 1 << endl;
    }

    return 0;
}

In file included from /usr/include/c++/4.8/unordered_set:35:0,
                 from answer.code:3:
/usr/include/c++/4.8/bits/c++0x_warning.h:32:2: error: #error This file requires compiler and library support for the ISO C++ 2011 standard. This support is currently experimental, and must be enabled with the -std=c++11 or -std=gnu++11 compiler options.
 #error This file requires compiler and library support for the \
  ^
answer.code:11:1: error: 'unordered_set' does not name a type
 unordered_se...