HDU1754 && HDU1166 线段树模板题

HDU1754

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=1754

题目分析：对于给出的一个很长的区间，对其进行单点更新值和区间求最大值的操作，由于查询的区间很大，且查询次数多，这里用线段树求解将是十分合适的

注意点：1.对于存放线段树的数组大小需要开大一些

　　　　2.对于c语言的字符输入%c之前需要加一个空格保证输入准确

 #include<iostream>
 #include<string.h>
 using namespace std;

 const int N = ;
 int grade[N];
 int tree[N<<];                    //这里建立的树的数组大小需要是N的4倍 否则不够用
 int n, m;

 int max(int a, int b){
     if(a > b) return a;
     else return b;
 }

 void build_tree(int start, int end, int node){                    //线段树的建立
     if(start == end){
         tree[node] = grade[start];
     }else{
         int mid = (start + end) / ;
         int left_node = node*;
         int right_node = node*+;

         build_tree(start, mid, left_node);
         build_tree(mid+, end, right_node);
         tree[node] = max(tree[left_node], tree[right_node]);
     }
 }

 void update_tree(int start, int end, int node, int index, int value){    //单点更新值
     if(start == end){
         tree[node] = value;
     }else{
         int mid = (start + end) / ;
         int left_node = node*;
         int right_node = node*+;

         if(index <= mid)
             update_tree(start, mid, left_node, index, value);
         else
             update_tree(mid+, end, right_node, index, value);
         tree[node] = max(tree[left_node], tree[right_node]);
     }
 }

 int search_tree(int start, int end, int node, int l, int r){        //区间查询最大值
     if(l > end || r < start){
         return ;
     }else if(l <= start && r >= end){
         return tree[node];
     }else if(start == end){　　　　　　//这里的个递归出口放在后面是有原因的，有可能存在start==end 但是l和r根本和start end没有交集的情况，所以先判去了后者
         return tree[node];
     }
     int mid = (start + end) / ;
     int left_node = node*;
     int right_node = node*+;

     int left_max = search_tree(start, mid, left_node, l, r);
     int right_max = search_tree(mid+, end, right_node, l, r);
     int ans = max(left_max, right_max);
     return ans;
 }

 int main(){
     while(scanf("%d%d", &n, &m) != EOF){
         for(int i = ; i <= n; i++)
             scanf("%d", &grade[i]);
         build_tree(, n, );
         for(int i = ; i <= m; i++){
             char c;
             int a, b;
             scanf(" %c %d %d", &c, &a, &b);            //对于c语言的输入字符在%c之前需要一个空格，否则c就读取不到需要的字符了
             if(c == 'U') update_tree(, n, , a, b);
             else{
                 int ans = search_tree(, n, , a, b);
                 printf("%d\n", ans);
             }
         }
     }
     return ;
 }

HDU1166

题目分析：

也是一题线段树的模板题，单点更新和区间查询求和（本质上和区间求最大值是一样的）

代码：

 #include<iostream>
 #include<string>
 #include<string.h>
 using namespace std;

 const int N = ;
 int peo[N];
 int tree[N<<];

 void build_tree(int start, int end, int node){
     if(start == end){
         tree[node] = peo[start];
     }else{
         int mid = (start + end) / ;
         int left_node = node*;
         int right_node = node*+;

         build_tree(start, mid, left_node);
         build_tree(mid+, end, right_node);
         tree[node] = tree[left_node] + tree[right_node];
     }
 }

 void update_tree(int start, int end, int node, int index, int value){
     if(start == end){
         tree[node] += value;
     }else{
         int mid = (start + end) / ;
         int left_node = node*;
         int right_node = node*+;

         if(index <= mid)
             update_tree(start, mid, left_node, index, value);
         else
             update_tree(mid+, end, right_node, index, value);
         tree[node] = tree[left_node] + tree[right_node];
     }
 }

 int query_tree(int start, int end, int node, int l, int r){
     if(end < l || start > r){
         return ;
     }else if(start >= l && end <= r){
         return tree[node];
     }else if(start == end){
         return tree[node];
     }
     int mid = (start + end)    / ;
     int left_node = node*;
     int right_node = node*+;

     int left_sum = query_tree(start, mid, left_node, l, r);
     int right_sum = query_tree(mid+, end, right_node, l, r);
     int ans = left_sum + right_sum;
     return ans;
 }

 int main(){
     int t;
     scanf("%d", &t);
     int cnt = ;
     while(t--){
         printf("Case %d:\n", cnt++);
         int n;
         scanf("%d", &n);
         for(int i = ; i <= n; i++)
             scanf("%d", &peo[i]);
         build_tree(, n, );
         string s;
         int a, b;
         while(cin>>s){
             if(s == "End") break;
             scanf("%d%d", &a, &b);
             if(s == "Query"){
                 int ans = query_tree(, n, , a, b);
                 printf("%d\n", ans);
             }
             if(s == "Add"){
                 update_tree(, n, , a, b);
             }
             if(s == "Sub"){
                 update_tree(, n, , a, -b);
             }
         }
     }
     return ;
 }