hdu1754 线段树

来源：互联网发布：淘宝店铺月销量怎么看编辑：程序博客网时间：2024/06/08 06:45

什么都不说了，贴代码，理解的时候画个树来理解理解就好了，这个也是典型的牺牲空间复杂度来缩短时间复杂度的典型算法。。。。

还是附点图上来吧。。。。。鼠标画的，见谅

#include<iostream>#include<cstdio>#include<cmath>#include<cstring>#define maxn 200005using namespace std;int a[maxn * 4];void build(int left, int right, int root){    if(left == right)        scanf("%d", &a[root]);    else    {        int mid = (left + right) / 2;        build(left, mid, root * 2);        build(mid + 1, right, root * 2 + 1);        a[root] = max(a[root * 2], a[root * 2 + 1]);    }}void up(int x, int y, int left, int right, int root){    if(left == right)        a[root] = y;    else    {        int mid = (left + right) / 2;        if(x <= mid)            up(x, y, left, mid, root * 2);        else            up(x, y, mid + 1, right, root * 2 + 1);        a[root] = max(a[root * 2], a[root * 2 + 1]);    }}int query(int x, int y, int left, int right, int root){    if(x <= left && y >= right)        return a[root];    else    {        int sum = 0;        int mid = (left + right) / 2;        if(x <= mid)            sum = max(sum, query(x, y, left, mid, root * 2));        if(y > mid)            sum = max(sum, query(x, y, mid + 1, right, root * 2 + 1));        return sum;    }}int main(){    int m, n;    while(scanf("%d%d", &n, &m) != EOF)    {        build(1, n, 1);        int x, y;        char c;        for(int i = 1; i <= 10; i ++)            cout << a[i] << endl;        getchar();        while(m --)        {            scanf("%c %d %d", &c, &x, &y);//            cout << c << ' ' << x << ' ' << y << endl;            getchar();            if(c == 'Q')                cout << query(x, y, 1, n, 1) << endl;            else                up(x, y, 1, n, 1);        }        memset(a, 0, sizeof(a));    }    return 0;}

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