HDU 1166 敵兵布陣(線段樹，區間求和)

連結：

http://acm.hdu.edu.cn/showproblem.php?pid=1166

分析與總結：

我的第一道線段樹，留做紀念。。

學習過程中，主要是遇到了一個問題：

在輸入初始化線段樹時，有的是直接在build函數裡面輸入，有的是在外面先全部輸入到一個數組裡面，然後才build，代碼如下：

1.  

int build(int cur, int left, int right){    t[cur].left  = left;    t[cur].right = right;    if(left == right){        // a數組為已經全部輸入完畢了        return t[cur].val=a[left];    }    int m = (left+right)>>1;    return t[cur].val = build(lson(cur),left,m)+build(rson(cur),m+1,right);}

2.

int build(int cur, int left, int right){    t[cur].left  = left;    t[cur].right = right;    if(left == right){        scanf("%d",&t[cur].val); //直接在這裡輸入        return t[cur].val;    }    int m = (left+right)>>1;    build(lson(cur),left,m);    build(rson(cur),m+1,right);    push_up(cur);}

然後我是綜合了上面兩種方式:

int build(int cur, int left, int right){    t[cur].left  = left;    t[cur].right = right;    if(left == right){        scanf("%d",&t[cur].val);        return t[cur].val;    }    int m = (left+right)>>1;    return t[cur].val = build(lson(cur),left,m)+build(rson(cur),m+1,right);}

結果一直WA.....    

最後發現不能直接return t[cur].val = build(lson(cur),left,m)+build(rson(cur),m+1,right); 

只能像第2中方式一樣。。。不知道為什麼。。求解。。

代碼：

1.  線段樹

#include<iostream>#include<cstring>#include<cstdio>#define lson(x) ((x)<<1)#define rson(x) (lson(x)|1)using namespace std;typedef int Type; const int MAX_NODE = 55555<<2; //開節點數的4倍大小struct node{    int left, right;     Type val;    int mid(){return (left+right)>>1;}    bool buttom(){return left==right;}};class SegTree{public:    void build(int cur,int left,int right){        t[cur].left  = left;        t[cur].right = right;        if(left==right) {            scanf("%d", &t[cur].val);            return;        }        int m = (left+right)>>1;        build(lson(cur),left,m);        build(rson(cur),m+1,right);        push_up(cur);    }    void update(int cur, int p, Type add){        t[cur].val += add;        if(t[cur].buttom())            return ;        int m=t[cur].mid();        if(p <= m)             update(lson(cur),p,add);        else            update(rson(cur),p,add);    }    int query(int cur,int left,int right){        if(t[cur].left==left && t[cur].right==right)            return t[cur].val;        int m = t[cur].mid();        if(right <= m)            return query(lson(cur),left,right);        else if(left > m)            return query(rson(cur),left,right);        else            return query(lson(cur),left,m)+query(rson(cur),m+1,right);    }private:    void push_up(int cur){        t[cur].val = t[lson(cur)].val+t[rson(cur)].val;     }    node t[MAX_NODE];};SegTree st;int main(){    int T,cas=1,n, x, y;    char cmd[8];    scanf("%d", &T);    while(T--){        printf("Case %d:\n",cas++);        scanf("%d",&n);        st.build(1,1,n);        while(scanf("%s",cmd)){            if(cmd[0]=='E')break;            scanf("%d%d",&x,&y);            if(cmd[0]=='A')                st.update(1,x,y);            else if(cmd[0]=='S')                st.update(1,x,-y);            else                 printf("%d\n",st.query(1,x,y));        }    }    return 0;}

2. 樹狀數組

#include<iostream>#include<cstdio>#include<cstring>#define mid ((left+right)>>1)#define lson rt<<1,left,mid#define rson rt<<1|1,mid+1,rightusing namespace std;const int MAXN = 50005;int c[MAXN], n;int lowbit(int x){return x&(-x);}int sum(int x){    int ret = 0;    while(x > 0){        ret += c[x];        x -= lowbit(x);    }    return ret;}void add(int x, int add){    while(x <= n){        c[x] += add;        x += lowbit(x);    }}int main(){    int T, x, y,cas=1;    char cmd[8];    scanf("%d",&T);    while(T--){        printf("Case %d:\n", cas++);        memset(c, 0, sizeof(c));        scanf("%d",&n);        for(int i=1; i<=n; ++i){            scanf("%d",&x);            add(i,x);        }        while(scanf("%s",cmd)){            if(cmd[0] == 'E') break;            scanf("%d %d",&x,&y);            if(cmd[0] == 'Q'){                printf("%d\n", sum(y)-sum(x-1));            }            else if(cmd[0] == 'A')                add(x,y);            else                add(x,-y);        }    }    return 0;}

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          原創 http://blog.csdn.net/shuangde800 ， By
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