HDU - 1754 I Hate It （线段树）

来源：互联网发布：电子元件查询软件 app 编辑：程序博客网时间：2024/06/03 18:38

解析：线段树模板题，线段树单点更新，找出区间最大值和更改区间点的值。

#include <cstdio>#include <cstring>#include <algorithm>using namespace std;const int N = 200000;int a[N];int s[N << 2], L[N << 2], R[N << 2];void build(int u,int l,int r) {if(l == r) {L[u] = R[u] = l;s[u] = a[l];return ;}int mid = (l + r) / 2;build(u*2,l,mid);build(u*2+1,mid+1,r);L[u] = l;R[u] = r;s[u] = max(s[u*2],s[u*2+1]);}void modify(int u,int x,int v) {if(R[u] == x && L[u] == x) {//叶子节点，找到结果返回s[u] = v;return ;}int mid = (L[u] + R[u]) / 2;if(x <= mid) {modify(u*2,x,v);}else {modify(u*2+1,x,v);}s[u] = max(s[u*2],s[u*2+1]);}int query(int u,int l,int r) {if(l <= L[u] && R[u] <= r) {return s[u];}int mid = (L[u] + R[u]) / 2;int ret = -N;if(l <= mid) {ret = max(ret,query(u*2,l,r));}if(r > mid) {ret = max(ret,query(u*2+1,l,r));}return ret;}int main() {int m,n;int x,y;while(scanf("%d%d",&n,&m) != EOF) {for(int i = 1; i <= n; i++) {scanf("%d",&a[i]);}memset(s,0,sizeof(s));L[1] = 1;R[1] = n;build(1,L[1],R[1]);char cmd[3];while(m--) {scanf("%s",cmd);if(cmd[0] == 'Q') {scanf("%d%d",&x,&y);printf("%d\n",query(1,x,y));}else if(cmd[0] == 'U') {scanf("%d%d",&x,&y);modify(1,x,y);}}}return 0;}

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