HDU 5200 Trees 二分

题目链接：

hdu:http://acm.hdu.edu.cn/showproblem.php?pid=5200

bc(中文):http://bestcoder.hdu.edu.cn/contests/contest_chineseproblem.php?cid=574&pid=1003

题解：

把输入按照高度排序，离线处理出所有高度的答案，每次查询的时候二分查找（upper_bound)。

 #include<iostream>
 #include<cstring>
 #include<cstdio>
 #include<algorithm>
 using namespace std;

 const int maxn = ;
 const int mod = 1e9 + ;
 typedef long long LL;

 struct Node {
     int id, h;
     bool operator < (const Node& rhm) const {
         return h<rhm.h;
     }
 }nds[maxn];

 int n, q;
 int ans[maxn];
 bool cuted[maxn];
 // int fa[maxn];

 void init() {
     // for(int i=0;i<maxn;i++) fa[i]=i;
     memset(cuted, , sizeof(cuted));
     cuted[] = cuted[n + ] = ;
 }

 int solve(int x) {
     //超出去的部分要先处理掉
     if (x<nds[].h) return ;
     if (x >= nds[n - ].h) return ;
     int low = , hig = n;
     while (low + <hig) {
         int mid = low + (hig - low) / ;
         if (nds[mid].h <= x) low = mid;
         else hig = mid;
     }
     return ans[low];
 }

 int main() {
     while (scanf("%d%d", &n, &q) ==  && n) {
         init();
         for (int i = ; i<n; i++) {
             scanf("%d", &nds[i].h);
             nds[i].id = i + ;
         }
         sort(nds, nds + n);
         int num = ;
         for (int i = ; i<n; i++) {
             int id = nds[i].id;
             if (!cuted[id - ] && !cuted[id + ]) {
                 num++;
             }
             else if (cuted[id - ] && cuted[id + ]) {
                 num--;
             }
             cuted[id] = ;
             ans[i] = num;
         }
         while (q--) {
             int x;
             scanf("%d", &x);
             printf("%d\n", solve(x));
         }
     }
     return ;
 }
 /*
 1 100
 1
 0
 2
 */

直接用upper_bound():

 #include<iostream>
 #include<cstring>
 #include<cstdio>
 #include<algorithm>
 using namespace std;

 const int maxn = ;
 const int mod = 1e9 + ;
 typedef long long LL;

 struct Node {
     int id, h;
     Node(int id, int h) :id(id), h(h) {}
     Node() {}
     bool operator < (const Node& rhm) const {
         return h<rhm.h;
     }
 }nds[maxn];

 int n, q;
 int ans[maxn];
 bool cuted[maxn];
 // int fa[maxn];

 void init() {
     // for(int i=0;i<maxn;i++) fa[i]=i;
     memset(cuted, , sizeof(cuted));
     cuted[] = cuted[n + ] = ;
 }

 int solve(int x) {
     //超出去的部分要先处理掉
     if (x<nds[].h) return ;
     if (x >= nds[n - ].h) return ;
     //upper_bound找到的是x后面的一个数，所以要减一
     return ans[upper_bound(nds, nds + n, Node(,x))-nds-];
 }

 int main() {
     while (scanf("%d%d", &n, &q) ==  && n) {
         init();
         for (int i = ; i<n; i++) {
             scanf("%d", &nds[i].h);
             nds[i].id = i + ;
         }
         sort(nds, nds + n);
         int num = ;
         for (int i = ; i<n; i++) {
             int id = nds[i].id;
             if (!cuted[id - ] && !cuted[id + ]) {
                 num++;
             }
             else if (cuted[id - ] && cuted[id + ]) {
                 num--;
             }
             cuted[id] = ;
             ans[i] = num;
         }
         while (q--) {
             int x;
             scanf("%d", &x);
             printf("%d\n", solve(x));
         }
     }
     return ;
 }
 /*
 1 100
 1
 0
 2
 */