HDU 1754 I hate it 线段树的应用

#include<stdio.h>



#define N_MAX 200010
typedef struct {
	int left,right;
	int maxScore;
}seg_tree;

seg_tree trees[N_MAX*4 +1];
int score[N_MAX+10];

int get_max(int x,int y){
	return x>y?x:y;
}
void build_tree(int root,int left,int right)
{
	trees[root].left = left;
	trees[root].right = right;
	if(left == right)
	{
		trees[root].maxScore = score[left];
		return ;
	}
	int mid = (left + right)>>1;
	build_tree(root*2,left,mid);
	build_tree(root*2+1,mid+1,right);
	trees[root].maxScore = get_max(trees[root*2].maxScore,trees[root*2+1].maxScore);
}

int find_max(int root,int left,int right)
{
	if(trees[root].left == left && trees[root].right == right )
	{
		return trees[root].maxScore;
	}
	int mid = (trees[root].left + trees[root].right)>>1;
	if(right <= mid)
	{
		return find_max(root*2,left,right);
	}
	if(left > mid)
	{
		return find_max(root*2+1,left,right);
	}
	
	return get_max(find_max(root*2,left,mid),find_max(root*2+1,mid+1,right));
}

void update(int root,int id,int new_value)
{
	if(trees[root].left  == trees[root].right)
	{
		trees[root].maxScore = new_value;
		return ;
	}
	int mid = (trees[root].left + trees[root].right)>>1;
	if(id <= mid)
		update(root*2,id, new_value);
	else
		update(root*2+1,id,new_value);

	trees[root].maxScore = get_max(trees[root*2].maxScore,trees[root*2+1].maxScore);
}

int
main(void)
{
	int N,M;
	while(scanf("%d %d",&N,&M) != EOF)
	{
		int i,j,k;
		char C;
		int A,B;

		for(i = 1;i<=N;i++)
			scanf("%d",&score[i]);

		build_tree(1,1,N);
		getchar();

		for(i = 1;i<=M;i++)
		{
			scanf("%c",&C);
			
			if(C == 'Q')
			{
				scanf("%d %d",&A,&B);
				printf("%d\n",find_max(1,A,B));
			}
			else{
				scanf("%d %d",&A,&B);
				update(1,A,B);
			}
			getchar();
		}
		
	}
	return 0;
}