hiho一下 第二十週 線段樹的區間修改

題目有了一些變化：查詢區間的總和；將區間內的值都修改爲指定值。

因此可以對之前的代碼進行修改，當修改的時候，修改所有被影響到的節點。但是這樣做會TLE，題目中給出了提示，修改的時候，如果搜到了符合條件的區間，本應該繼續向下修改，但是我們不往下搜了，用一個lazytag來標記這個節點，等到以後要用它的子節點的時候，再用lazytag更新左右孩子節點，這樣就會節省時間。

TLE代碼：

#include <stdio.h> 
  
int ST[2097152];//最多2^21-1個節點，注意不是2*N-1個節點，[0]不用
int N, A, B;   

int Query(){
	int l, r, sum;
	
	scanf("%d%d", &l, &r);
	l = l + A - 1;
	r = r + A - 1;
	sum = 0;
	while(1){
		if(l == r){
			sum += ST[l];
			break;
		}
		if(l&1){//若l是奇數 
			sum += ST[l];
			l++;
		}
		if((r&1) == 0){//若r是偶數 
			sum += ST[r];
			r--;
		}
		l >>= 1;
		r >>= 1;
	}
	return sum;
}

void Update(){
	int l, r, v, i;
	
	scanf("%d%d%d", &l, &r, &v);
	l = l + A - 1;
	r = r + A - 1;
	for(i = l; i <= r; i++){
		ST[i] = v;
	}
	l >>= 1;
	r >>= 1;
	while(l){
		for(i = l; i <= r; i++){
			ST[i] = ST[l << 1] + ST[(l << 1) + 1];
		}
		l >>= 1;
		r >>= 1;
	}
}
  
int main(){  
    int Q, i, ans, a;
      
    scanf("%d", &N);  
    for(A = 1; A < N; A <<= 1);  
    for(i = A; i < A+N; i++){  
        scanf("%d", &ST[i]);  
    }  
    for(i = A+N, B = A << 1; i < B; i++){  
        ST[i] = 0;  
    }  
    //build segment tree  
    for(i = A-1; i; i--){  
        ST[i] = ST[i << 1] + ST[(i << 1) + 1];  
    }  
      
    scanf("%d", &Q);  
    while(Q--){  
        scanf("%d", &a);  
        if(a == 0){  
            printf("%d\n", Query());  
        }else{  
            Update();
        }  
    }  
    return 0;  
} 

AC代碼：

#include <stdio.h>  
#include <stdlib.h>  
#define MAX_N 100000  
  
typedef struct NODE{  
    struct NODE *left, *right;  
    int value, lazytag;  
}Node;  
  
Node* Creat(int i, int j){  
    Node *p = (Node*)malloc(sizeof(Node));  
    if(i == j){  
        p -> left = NULL;  
        p -> right = NULL;  
        scanf("%d", & p -> value);  
    }else{  
        p -> left = Creat(i, (i+j)/2);  
        p -> right = Creat((i+j)/2+1, j);  
        p -> value = p -> left -> value + p -> right -> value;  
    }  
    p -> lazytag = -1;
    return p;  
}  
  
//深度搜索並更新   
void Adjust(Node *p, int l, int r, int i, int j, int v){//搜索節點，節點區間，修改區間，修改值   
    if(l == i && r == j){  
        p -> lazytag = v;
		p -> value = (r - l + 1) * v;  
        return;  
    }  
    
    int mid = (l+r)/2, temp;  
    
    if(p -> lazytag != -1){//檢查並處理lazytag
    	p -> left -> lazytag = p -> lazytag;
		p -> left -> value = p -> lazytag * (mid - l + 1);
		
		p -> right -> lazytag = p -> lazytag;
		p -> right -> value = p -> lazytag * (r - mid);
		
		p -> lazytag = -1;
    }
    
    if(j <= mid){  
        Adjust(p -> left, l, mid, i, j, v);  
    }else if(i > mid){  
        Adjust(p -> right, mid+1, r, i, j, v);  
    }else{
    	Adjust(p -> left, l, mid, i, mid, v);
    	Adjust(p -> right, mid+1, r, mid+1, j, v);
    }
    
    p -> value = p -> left -> value + p -> right -> value;  
}  
  
int Query(Node* p, int l, int r, int i, int j){//查詢的節點，節點代表的區間，查詢的區間   
    if(i == l && j == r){  
        return p -> value;  
    }  
    
    int mid = (l + r)/2;  
    
	if(p -> lazytag != -1){//檢查並處理lazytag
		p -> left -> lazytag = p -> lazytag;
		p -> left -> value = p -> lazytag * (mid - l + 1);
		
		p -> right -> lazytag = p -> lazytag;
		p -> right -> value = p -> lazytag * (r - mid);
		
		p -> lazytag = -1;
	}
	
    if(j <= mid){  
        return Query(p -> left, l, mid, i, j);  
    }  
    if(i >= mid + 1){  
        return Query(p -> right, mid+1, r, i, j);  
    }  
    
    return Query(p -> left, l, mid, i, mid) + Query(p -> right, mid+1, r, mid + 1, j);  
}  
  
int main(){  
    int n, i, Q, a, b, c, d;  
    Node *root;  
      
    scanf("%d", &n);  
    root = Creat(1, n);  
      
    scanf("%d", &Q);  
    while(Q--){  
        scanf("%d%d%d", &a, &b, &c);  
        if(a == 0){  
            printf("%d\n", Query(root, 1, n, b, c));  
        }else{  
        	scanf("%d", &d);
            Adjust(root, 1, n, b, c, d);   
        }  
    }  
      
    return 0;  
}