输入描述:

第一行输入 n,Q。
第二行输入 n 个数，表示 a 数组。
接下来 Q 行，每行输入 L,R。
1<=n,Q<=500000,0<=a[i]<=1000000,1<=L<=R<=n

输出描述:

若有解，输出 r-l+1 最小是多少。
否则输出“-1”。

4 2

2 1 3 3

1 2

1 3

-1

3

第一次询问无解。
第二次询问:
l=1,r=3

#pragma comment(linker, "/STACK:1024000000,1024000000")

#include <cstdio>

#include <string>

#include <cstdlib>

#include <cmath>

#include <iostream>

#include <cstring>

#include <set>

#include <queue>

#include <algorithm>

#include <vector>

#include <map>

#include <cctype>

#include <cmath>

#include <stack>

#include <sstream>

#include <list>

#include <assert.h>

#include <bitset>

#include <numeric>

#define debug() puts("++++")

#define gcd(a, b) __gcd(a, b)

#define lson l,m,rt<<1

#define rson m+1,r,rt<<1|1

#define fi first

#define se second

#define pb push_back

#define sqr(x) ((x)*(x))

#define ms(a,b) memset(a, b, sizeof a)

#define sz size()

#define be begin()

#define ed end()

#define pu push_up

#define pd push_down

#define cl clear()

#define lowbit(x) -x&x

#define all 1,n,1

#define FOR(i,n,x)  for(int i = (x); i < (n); ++i)

#define freopenr freopen("in.in", "r", stdin)

#define freopenw freopen("out.out", "w", stdout)

using namespace std;

typedef long long LL;

typedef unsigned long long ULL;

typedef pair<int, int> P;

const int INF = 0x3f3f3f3f;

const LL LNF = 1e17;

const double inf = 1e20;

const double PI = acos(-1.0);

const double eps = 1e-8;

const int maxn = 5e5 + 7;

const int maxm = 2000000 + 7;

const LL mod = 1e9 + 7;

const int dr[] = {-1, 1, 0, 0, 1, 1, -1, -1};

const int dc[] = {0, 0, 1, -1, 1, -1, 1, -1};

const char *de[] = {"0000", "0001", "0010", "0011", "0100", "0101", "0110", "0111", "1000", "1001", "1010", "1011", "1100", "1101", "1110", "1111"};

int n, m;

const int mon[] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

const int monn[] = {0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

inline bool is_in(int r, int c) {

  return r >= 0 && r < n && c >= 0 && c < m;

}

inline int readInt(){ int x;  scanf("%d", &x);  return x; }

int a[maxn];

int sum[maxn<<2];

void update(int M, int val, int l, int r, int rt){

  if(l == r){

    sum[rt] = val;

    return ;

  }

  int m = l + r >> 1;

  if(M <= m)  update(M, val, lson);

  else  update(M, val, rson);

  sum[rt] = min(sum[rt<<1], sum[rt<<1|1]);

}

int query(int L, int R, int l, int r, int rt){

  if(L <= l && r <= R)  return sum[rt];

  int ans = INF;

  int m = l + r >> 1;

  if(L <= m)  ans = query(L, R, lson);

  if(R > m)  ans = min(ans, query(L, R, rson));

  return ans;

}

struct Query{

  int id, l, r;

};

int ans[maxn];

Query q[maxn];

int main(){

  scanf("%d %d", &n, &m);

  ms(sum, INF);

  int sum = 0;

  map<int, int> mp;  mp[0] = 1;

  ms(a, INF);

  for(int i = 1; i <= n; ++i){

    int x;  scanf("%d", &x);

    sum ^= x;

    int y = mp[sum];

    if(y != 0)  a[i] = y;

    mp[sum] = i+1;

  }

  for(int i = 0; i < m; ++i){

    q[i].id = i;

    scanf("%d %d", &q[i].l, &q[i].r);

  }

  sort(q, q + m, [&](Query q1, Query q2){ return q1.r < q2.r; });

  int x = 1;

  for(int i = 0; i < m; ++i){

    while(x <= q[i].r){

      if(a[x] != INF)  update(a[x], x-a[x]+1, all);

      ++x;

    }

    int res = query(q[i].l, q[i].r, all);

    ans[q[i].id] = res == INF ? -1 : res;

  }

  for(int i = 0; i < m; ++i)  printf("%d\n", ans[i]);

  return 0;

}