題目大意:給出n個數,現在要求求出區間中的第k大值
思路:劃分樹模版
#include <cstdio>
#include <algorithm>
#define N 100002
using namespace std;
struct node
{
int num[N], val[N];
}t[1000];//記錄每層的劃分
int n = 0, m = 0, ans = 0, srt[N];
void build_tree(int l, int r, int cur)
{
int m = (l+(r-l)/2), mid = 0, left_num = 0;
int s1 = l, s2 = m+1, c1 = 0, c2 = 0;//s1爲下一層分人左邊數開始存的地方, s2爲分入右邊第開始
if(l == r) return ;
mid = srt[m];
for(int i = l; i<=r; i++) if(t[cur].val[i]<mid) c2++;//共有多少個進入左邊的
left_num = m-l+1-c2;//爲有多少個值等於mid時可以進左邊的
for(int i = l; i<=r; i++)//選出左右邊的部分
{
if(i == l) t[cur].num[i] = 0;
else t[cur].num[i] = t[cur].num[i-1];
if(t[cur].val[i]<mid)//小於進入左邊
{
t[cur].num[i]++;
t[cur+1].val[s1++] = t[cur].val[i];
}
else if(t[cur].val[i]==mid && c1<left_num)
{
c1++;
t[cur].num[i]++;
t[cur+1].val[s1++] = t[cur].val[i];
}
else
t[cur+1].val[s2++] = t[cur].val[i];
}
build_tree(l, m, cur+1);
build_tree(m+1, r, cur+1);
}//ok
void query(int a, int b, int k, int l, int r, int cur)
{
int m = (l+(r-l)/2);
if(a == b){ans = t[cur].val[a]; return ;}
int x = t[cur].num[a-1], y = t[cur].num[b];
if(a == l) x = 0;
if(y-x>=k)
query(l+x, l+y-1, k, l, m, cur+1);//進入左邊進行查詢
else
{
k = k-(y-x);
int s1 = a-l-x, s2 = (b-a+1)-(y-x);
if(a == l) s1 = 0;
query(m+1+s1, m+s2+s1, k, m+1, r, cur+1);//進入右邊進行查詢
}
}
int main()
{
int i = 0, a = 0, b = 0, k = 0;
while(scanf("%d %d", &n, &m) != EOF)
{
for(i = 1; i<=n; i++)
{
scanf("%d", &t[1].val[i]);
srt[i] = t[1].val[i];
}
sort(srt+1, srt+n+1);
build_tree(1, n, 1);
while(m--)
{
scanf("%d %d %d", &a, &b, &k);
query(a, b, k, 1, n, 1);
printf("%d\n", ans);
}
}
return 0;
}