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 = 200005;
int grade[N];
int tree[N<<2];                    //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) / 2;
        int left_node = node*2;
        int right_node = node*2+1;
        
        build_tree(start, mid, left_node);
        build_tree(mid+1, 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) / 2;
        int left_node = node*2;
        int right_node = node*2+1;
        
        if(index <= mid)
            update_tree(start, mid, left_node, index, value);
        else
            update_tree(mid+1, 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 0;
    }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) / 2;
    int left_node = node*2;
    int right_node = node*2+1;
    
    int left_max = search_tree(start, mid, left_node, l, r);
    int right_max = search_tree(mid+1, 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 = 1; i <= n; i++)
            scanf("%d", &grade[i]);
        build_tree(1, n, 1);    
        for(int i = 1; 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(1, n, 1, a, b);
            else{
                int ans = search_tree(1, n, 1, a, b);
                printf("%d\n", ans);
            }
        }
    }    
    return 0;
}

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 = 500005;
int peo[N];
int tree[N<<2];

void build_tree(int start, int end, int node){
    if(start == end){
        tree[node] = peo[start];
    }else{
        int mid = (start + end) / 2;
        int left_node = node*2;
        int right_node = node*2+1;
        
        build_tree(start, mid, left_node);
        build_tree(mid+1, 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) / 2;
        int left_node = node*2;
        int right_node = node*2+1;
        
        if(index <= mid)
            update_tree(start, mid, left_node, index, value);
        else
            update_tree(mid+1, 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 0;
    }else if(start >= l && end <= r){
        return tree[node];
    }else if(start == end){
        return tree[node];
    }
    int mid = (start + end)    / 2;
    int left_node = node*2;
    int right_node = node*2+1;
    
    int left_sum = query_tree(start, mid, left_node, l, r);
    int right_sum = query_tree(mid+1, end, right_node, l, r);
    int ans = left_sum + right_sum;
    return ans;
}

int main(){
    int t;
    scanf("%d", &t);
    int cnt = 1;
    while(t--){
        printf("Case %d:\n", cnt++);
        int n;
        scanf("%d", &n);
        for(int i = 1; i <= n; i++)
            scanf("%d", &peo[i]);
        build_tree(1, n, 1);
        string s;
        int a, b;
        while(cin>>s){
            if(s == "End") break;
            scanf("%d%d", &a, &b);
            if(s == "Query"){
                int ans = query_tree(1, n, 1, a, b);    
                printf("%d\n", ans);
            }
            if(s == "Add"){
                update_tree(1, n, 1, a, b);
            }
            if(s == "Sub"){
                update_tree(1, n, 1, a, -b);
            }
        }
    }
    return 0;
}