【POJ2104】【整体二分+树状数组】区间第k大

  1 /*
  2 宋代郑思肖
  3 《画菊》
  4 花开不并百花丛，独立疏篱趣未穷。
  5 宁可枝头抱香死，何曾吹落北风中。
  6 */
  7 #include <iostream>
  8 #include <cstdio>
  9 #include <algorithm>
 10 #include <cstring>
 11 #include <vector>
 12 #include <utility>
 13 #include <iomanip>
 14 #include <string>
 15 #include <cmath>
 16 #include <queue>
 17 #include <assert.h>
 18 #include <map>
 19 #include <ctime>
 20 #include <cstdlib>
 21 #include <stack>
 22 #define LOCAL
 23 const int MAXN = 100000 + 10;
 24 const int MAXM = 5000 + 10;
 25 const int INF = 0x7fffffff;
 26 const int SIZE = 450;
 27 const int maxnode =  250005 + 10;
 28 using namespace std;
 29 typedef long long ll;
 30 using namespace std;
 31 struct DATA{
 32        int val, x;//x代表位置 
 33        bool operator < (const DATA &b)const{
 34             return val < b.val;
 35        }
 36 }data[MAXN]; 
 37 struct QUESTION{
 38        int l, r;
 39        int k;
 40 }q[MAXM];
 41 int c[MAXN], id[MAXN], Ans[MAXN];
 42 int tmp[MAXN];
 43 bool mark[MAXN];
 44 int Max = -INF, Min = INF, pos, n, m;
 45 //树状数组 
 46 inline int lowbit(int x){return x&-x;}
 47 int sum(int x){
 48     int tmp = 0;
 49     while (x > 0){
 50           tmp += c[x];
 51           x -= lowbit(x);
 52     }
 53     return tmp;
 54 }
 55 void add(int x, int val){
 56      while (x <= n){
 57            c[x] += val;
 58            x += lowbit(x);
 59      }
 60      return;
 61 }
 62 
 63 void init(){
 64      memset(mark, 0, sizeof(mark));
 65      memset(c, 0, sizeof(c)); 
 66      scanf("%d%d", &n, &m);
 67      for (int i = 1; i <= n; i++){
 68          scanf("%d", &data[i].val);
 69          data[i].x = i;
 70          Max = max(Max, data[i].val);
 71          Min = min(Min, data[i].val);
 72      }
 73      //排序 
 74      sort(data + 1, data + 1 + n);
 75 }
 76 void solve(int l, int r, int L, int R){
 77       if (l > r || L == R) return;
 78       int mid = (L + R) >> 1;
 79       while (data[pos + 1].val <= mid && pos < n){
 80             add(data[pos + 1].x, 1);
 81             pos++;
 82       } 
 83       while (data[pos].val > mid){
 84             add(data[pos].x, -1);
 85             pos--;
 86       }
 87       int cnt = 0;//记录找到答案的回答个数 
 88       for (int i = l; i <= r; i++){
 89           if (sum(q[id[i]].r) - sum(q[id[i]].l - 1) > q[id[i]].k - 1){
 90              Ans[id[i]] = mid;
 91              mark[i] = 1;
 92              cnt++;
 93           }else mark[i] = 0;
 94       } 
 95       int l1 = l, l2 = l + cnt;
 96       for (int i = l; i <= r; i++)
 97       if (mark[i]) tmp[l1++] = id[i];
 98       else tmp[l2++] = id[i];
 99       
100       for (int i = l; i <= r; i++) id[i] = tmp[i];
101       solve(l, l1 - 1, L, mid);
102       solve(l1, l2 - 1, mid + 1, R);
103 }
104 void work(){
105      pos = 0;//初始化即data中的下标 
106      for (int i = 1; i <= m; i++){
107          scanf("%d%d%d", &q[i].l, &q[i].r, &q[i].k);
108      }
109      for (int i = 1; i <= m; i++) id[i] = i;
110      solve(1, m, Min, Max + 1);
111      for (int i = 1; i <= m; i++) printf("%d\n", Ans[i]);
112 }
113 
114 int main(){
115    
116     init();
117     work(); 
118     return 0;
119 }