HDU 1754 I Hate It

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

维护区间的最大值，使用线段树的单点更新。

#include <map>#include <stdio.h>#include <string.h>#include <iostream>#include <algorithm>using namespace std;const int MAX = 200000;struct node{    int l,r;    int value;    int mid(){        return (l + r) >> 1;    }}tree[MAX * 4];void buildtree(int l, int r, int rt){    tree[rt].l = l;    tree[rt].r = r;    if(l == r){        scanf("%d",&tree[rt].value);        return;    }    int mid = tree[rt].mid();    buildtree(l, mid, rt << 1);    buildtree(mid + 1, r, rt << 1 | 1);    tree[rt].value = max(tree[rt << 1].value, tree[rt << 1 | 1].value);}void update(int rt, int pos, int key){    if(tree[rt].l == pos && tree[rt].r == pos){        tree[rt].value = key;        return;    }    int mid = tree[rt].mid();    if(pos <= mid)        update(rt << 1, pos, key);    else    update(rt << 1 | 1, pos, key);    tree[rt].value = max(tree[rt << 1].value, tree[rt << 1 | 1].value);}int query(int rt, int a, int b){    if(a <= tree[rt].l && b >= tree[rt].r)        return tree[rt].value;    int mid = tree[rt].mid();    if(b <= mid)        query(rt << 1, a, b);    else if(a > mid)        query(rt << 1 | 1 , a, b);    else        return max(query(rt << 1, a, mid), query(rt << 1 | 1 , mid + 1, b));}int main(){//    freopen("in.txt", "r", stdin);    int N,M;    while(scanf("%d%d",&N,&M) != EOF){        buildtree(1, N, 1);        char ch;        while(M--){            getchar();            scanf("%c",&ch);            int a,b;            scanf("%d%d",&a,&b);            if(ch == 'Q'){                int ans = query(1, a, b);                printf("%d\n",ans);            }            else    update(1, a, b);        }    }    return 0;}

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