线段树之离散化
POJ - 2528
离散化是将有用的信息提取出来，在区间很大的时候，用直接用线段树肯定会超时，但由于在区间内很大值是没有用到的，只把有用的区间提取出来再用线段数做就方便多了。
1 #include <iostream> 2 #include <stdio.h> 3 #include <string.h> 4 #include <algorithm> 5 #define lson l,m,rt<<1 6 #define rson m+1,r,rt<<1|1 7 using namespace std; 8 const int MAX = 11111; 9 int col[MAX<<4],li[MAX],ri[MAX],x[MAX*3],ans; 10 bool hash[MAX]; 11 void PushDown(int rt){ 12 if(col[rt] != -1){ 13 col[rt<<1] = col[rt<<1|1] = col[rt]; 14 col[rt] = -1; 15 } 16 } 17 void update(int LL, int RR, int c, int l, int r, int rt){ 18 if(LL <= l && r <= RR){ 19 col[rt] = c; 20 return; 21 } 22 PushDown(rt); 23 int m = (l+r)>>1; 24 if(LL <= m)update(LL,RR,c,lson); 25 if(m < RR) update(LL,RR,c,rson); 26 } 27 void query(int l, int r, int rt){ 28 if(col[rt] != -1){ 29 if(!hash[col[rt]])ans++; 30 hash[col[rt]] = true; 31 return; 32 } 33 if(l == r)return; 34 int m = (l+r)>>1; 35 query(lson); 36 query(rson); 37 } 38 int Bin(int key,int len){ 39 int l = 0, r = len-1; 40 while(l <= r){ 41 int m = (l+r)>>1; 42 if(x[m] == key)return m; 43 if(x[m] > key)r = m-1; 44 else l = m+1; 45 } 46 return -1; 47 } 48 int main(){ 49 int t,n; 50 scanf("%d",&t); 51 while(t--){ 52 scanf("%d",&n); 53 int nn = 0; 54 for(int i = 0; i < n; i ++){ 55 scanf("%d %d",&li[i],&ri[i]); 56 x[nn++] = li[i];x[nn++] = ri[i]; 57 } 58 sort(x,x+nn); 59 int m = 1; 60 for(int i = 1; i < nn; i ++){ 61 if(x[i]!=x[i-1])x[m++] = x[i]; 62 } 63 for(int i = m-1; i > 0; i --){ 64 if(x[i] != x[i-1]+1)x[m++] = x[i-1]+1; 65 } 66 sort(x,x+m); 67 memset(col,-1,sizeof(col)); 68 for(int i = 0; i < n; i ++){ 69 int l = Bin(li[i],m); 70 int r = Bin(ri[i],m); 71 update(l,r,i,0,m,1); 72 } 73 ans = 0; 74 memset(hash,false,sizeof(hash)); 75 query(0,m,1); 76 printf("%d\n",ans); 77 } 78 return 0; 79 }
