问求每个点距离平方的最小的点
kd-tree模板题……
1 #include<bits/stdc++.h> 2 #define cl(a,b) memset(a,b,sizeof(a)) 3 #define debug(x) cerr<<#x<<"=="<<(x)<<endl 4 using namespace std; 5 typedef long long ll; 6 typedef pair<int,int> pii; 7 8 #define inf (1e9+20) 9 #define ll long long 10 #define ls ch[x][0] 11 #define rs ch[x][1] 12 13 const int maxn = 2e5+10; 14 15 struct P 16 { 17 int a[2] , num; 18 ll dis; 19 } p[maxn]; 20 21 int now , k = 2; 22 23 bool cmp(int a,int b) 24 { 25 return p[a].a[now] < p[b].a[now]; 26 } 27 28 ll dist(P a,P b) 29 { 30 ll sum = 0; 31 for(int i=0; i<k; i++) 32 { 33 sum += 1ll*(a.a[i]-b.a[i])*(a.a[i]-b.a[i]); 34 } 35 return sum; 36 } 37 38 int ch[maxn][2] , co[maxn] , root; 39 40 void pushup(int x) 41 { 42 co[x] = co[ls] + co[rs] + 1; 43 } 44 45 const double alp = 0.75; 46 47 bool isbad(int x) 48 { 49 return max(co[ls],co[rs]) > alp*co[x] + 5; 50 } 51 52 void build(int &x,int l,int r,int a[],int no) 53 { 54 if( l > r ) 55 { 56 x = 0; 57 return ; 58 } 59 int mid = l+r>>1; 60 now = no; 61 nth_element(a+l,a+mid,a+r+1,cmp); 62 x = a[mid]; 63 build(ls,l,mid-1,a,no^1); 64 build(rs,mid+1,r,a,no^1); 65 pushup(x); 66 } 67 68 P ans; 69 70 void Find(int x,int y,int no) 71 { 72 if(!x) return ; 73 ll dis = dist(p[y],p[x]); 74 if( x != y ) 75 { 76 if( dis < ans.dis || (dis==ans.dis&&p[x].num < ans.num) ) 77 { 78 ans = p[x]; 79 ans.dis = dis; 80 } 81 } 82 ll d = p[y].a[no] - p[x].a[no]; 83 Find(ch[x][d>0],y,no^1); 84 if( d*d <= ans.dis ) 85 {//找平方 86 Find(ch[x][d<=0],y,no^1); 87 } 88 } 89 90 int Fa , No; 91 92 int Insert(int &x,int fa,int k,int no) 93 { 94 if( x == 0 ) 95 { 96 x = k; 97 return 0; 98 } 99 int t = p[x].a[no]<p[k].a[no]; 100 int r = Insert(ch[x][t],x,k,no^1); 101 pushup(x); 102 if( isbad(x) ) r = x , Fa = fa , No = no; 103 return r; 104 } 105 106 int su[maxn] , len; 107 108 void travel(int x) 109 { 110 if(x==0) return ; 111 travel(ls); 112 su[len++] = x; 113 travel(rs); 114 } 115 116 void Insert(int k) 117 { 118 int x = Insert(root,0,k,0); 119 if(x) 120 { 121 int tmp = x; 122 len = 0; 123 travel(x); 124 build(x,0,len-1,su,No); 125 if(Fa) ch[Fa][ch[Fa][1]==tmp] = x; 126 else root = x; 127 } 128 } 129 130 int si; 131 132 void newnode(int x,int y,int id) 133 { 134 si++; 135 p[si].a[0] = x; 136 p[si].a[1] = y; 137 p[si].num = id; 138 ch[si][0] = ch[si][1] = 0; 139 co[si] = 1; 140 } 141 142 void init() 143 { 144 si = 0; 145 ch[0][0] = ch[0][1] = 0; 146 co[0] = 0; 147 root = 0; 148 } 149 150 int num[maxn]; 151 152 int main() 153 { 154 // freopen("in.txt","r",stdin); 155 int T,n; 156 scanf("%d",&T); 157 while(T--) 158 { 159 scanf("%d",&n); 160 init(); 161 int x,y; 162 for(int i=1; i<=n; i++) 163 { 164 scanf("%d%d",&x,&y); 165 newnode(x,y,i); 166 Insert(si); 167 } 168 for(int i=1; i<=n; i++) 169 { 170 ans.dis = 4e18; 171 Find(root,i,0); 172 printf("%lld ",ans.dis); 173 } 174 } 175 return 0; 176 }/* 177 178 2 179 10 180 17 41 181 0 34 182 24 19 183 8 28 184 14 12 185 45 5 186 27 31 187 41 11 188 42 45 189 36 27 190 15 191 0 0 192 1 2 193 2 3 194 3 2 195 4 0 196 8 4 197 7 4 198 6 3 199 6 1 200 8 0 201 11 0 202 12 2 203 13 1 204 14 2 205 15 0 206 207 */