题目链接：http://poj.org/problem?id=3264
查找区间最值，做差。
1 #include<cstdio> 2 #include<iostream> 3 #define lson l,m,rt<<1 4 #define rson m+1,r,rt<<1|1 5 #define ll long long 6 using namespace std; 7 const int maxn=50010; 8 int f[maxn<<2]; 9 int k[maxn<<2]; 10 11 inline void pushup(int rt) 12 { 13 f[rt]=max(f[rt<<1],f[rt<<1|1]); 14 k[rt]=min(k[rt<<1],k[rt<<1|1]); 15 } 16 17 void build(int l,int r,int rt) 18 { 19 if(l==r) 20 { 21 scanf("%lld",&f[rt]); 22 k[rt]=f[rt]; 23 return; 24 } 25 int m=(l+r)>>1; 26 build(lson); 27 build(rson); 28 pushup(rt); 29 } 30 31 int querymax(int L,int R,int l,int r,int rt) 32 { 33 if(L<=l&&r<=R) return f[rt]; 34 int m=(l+r)>>1; 35 int ans=-1; 36 if(L<=m) ans=max(ans,querymax(L,R,lson)); 37 if(m<R) ans=max(ans,querymax(L,R,rson)); 38 return ans; 39 } 40 int querymin(int L,int R,int l,int r,int rt) 41 { 42 if(L<=l&&r<=R) return k[rt]; 43 int m=(l+r)>>1; 44 int ans=99999999999; 45 if(L<=m) ans=min(ans,querymin(L,R,lson)); 46 if(m<R) ans=min(ans,querymin(L,R,rson)); 47 return ans; 48 } 49 int main() 50 { 51 int n,m; 52 while(scanf("%d%d",&n,&m)!=EOF) 53 { 54 build(1,n,1); 55 while(m--) 56 { 57 int a,b; 58 scanf("%d%d",&a,&b); 59 int M=querymax(a,b,1,n,1); 60 int mm=querymin(a,b,1,n,1); 61 printf("%d ",M-mm); 62 } 63 } 64 }
刚学了RMQ，方便很多。。。
1 #include<cstdio> 2 #include<cstring> 3 #include<algorithm> 4 #include<cmath> 5 using namespace std; 6 const int maxn=500010; 7 8 int maxx[maxn][25],minn[maxn][25]; 9 int a[maxn]; 10 int n,m; 11 void RMQ_INIT(int n) 12 { 13 int k=log(n+0.0)/log(2.0); 14 for(int i=0;i<n;i++) 15 { 16 maxx[i][0]=a[i]; 17 minn[i][0]=a[i]; 18 } 19 for(int j=1;j<=k;j++) 20 for(int i=0;i+(1<<j)-1<n;i++) 21 { 22 maxx[i][j]=max(maxx[i][j-1],maxx[i+(1<<j-1)][j-1]); 23 minn[i][j]=min(minn[i][j-1],minn[i+(1<<j-1)][j-1]); 24 } 25 return ; 26 } 27 int rmq(int x,int y) 28 { 29 int k=log(y*1.0-x+1)/log(2.0); 30 int a=max(maxx[x][k],maxx[y-(1<<k)+1][k]); 31 int b=min(minn[x][k],minn[y-(1<<k)+1][k]); 32 return a-b; 33 } 34 int main() 35 { 36 while(scanf("%d%d",&n,&m)!=EOF) 37 { 38 for(int i=0;i<n;i++) 39 scanf("%d",&a[i]); 40 RMQ_INIT(n); 41 while(m--) 42 { 43 int u,v; 44 scanf("%d%d",&u,&v); 45 u--; 46 v--; 47 printf("%d ",rmq(u,v)); 48 } 49 } 50 }