HDU - 1754 I Hate It(线段树，单点修改)

题目大意：中文题

解题思路：模版题

#include
#include
#include
using namespace std;
const int maxn = 200000 << 2;
int S[maxn], L[maxn], R[maxn];
int num[maxn];
void build(int u, int l, int r) {

    if( l == r) {
        S[u] = num[l];  
        L[u] = l;
        R[u] = l;
        return ;
    }
    int mid = (l + r) / 2;
    build(2*u,l,mid);
    build(2*u+1,mid+1,r);
    S[u] = max(S[2*u],S[2*u+1]);
    L[u] = l;
    R[u] = r;
}

void modify(int id, int x, int u) {
    if(L[x] == id && R[x] == id)  {
        S[x] = u;
        return ;
    }

    int mid = (L[x] + R[x]) / 2;
    if(id <= mid)  
        modify(id,2*x,u); 
    else
        modify(id,2*x+1,u);

    S[x] = max(S[2*x],S[2*x+1]);
}

int search(int s, int e, int u) {

    if(L[u] >= s && R[u] <= e) 
        return S[u];    

    int mid = (L[u] + R[u]) / 2;

    if(s >= mid + 1)  
        return search(s,e,2*u+1);
    else if(e <= mid) 
        return search(s,e,2*u);
    else
        return max(search(s,e,2*u),search(s,e,2*u+1));
}

int main() {
    int N, M;
    int test;
    while(scanf("%d%d",&N,&M) == 2) {
        for(int i = 1; i <= N; i++)
            scanf("%d",&num[i]);
        build(1,1,N);
        getchar();
        int s, e;
        char c;
        for(int i = 0; i < M; i++) {
            scanf("%c%d%d",&c,&s,&e);   
            getchar();
            if(c == 'Q')
                printf("%d\n",search(s,e,1));
            else
                modify(s,1,e);
        }

    }
    return 0;
}