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;

}