UVA 11234 - Expressions 二叉树建树+BFS 层次遍历

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给出了一个后缀表达式要给出用队列表示时的答案看simple output 知道输出时按照数的层数从下到上从右到左一一输出的

#include<cstdlib>#include<algorithm>#include<cctype>#include<stack>#include<cstdio>#include<cstring>#include<queue>using namespace std;int maxn = 10005;typedef struct TNode{    char v;    struct TNode *l,*r;//左节点右节点}Node;stack<Node*> st;queue<Node*> q;Node* newnode(){    Node* u = (Node*)malloc(sizeof(Node));    if(u != NULL)        u->l = u->r = NULL;    return u;}void addnode(char* s){    while(!st.empty())st.pop();    Node* u;    for(int i = 0; i < strlen(s); i++)    {        if(islower(s[i]))        {            u = newnode();            u->v = s[i];            st.push(u);        }        else        {            u = newnode();            u->r = st.top();            st.pop();            u->l = st.top();            st.pop();             u->v = s[i];            st.push(u);        }    }}int n = 0;void  BFS()//层次遍历{    while(!q.empty())q.pop();    char p[maxn];    memset(p,0,sizeof(p));    q.push(st.top());    while(!q.empty())    {        Node* u = q.front();        q.pop();        p[n++] = u->v;        if(u->l != NULL) q.push(u->l);        if(u->r != NULL) q.push(u->r);    }    for(int i = n-1; i >= 0;i --)        printf("%c",p[i]);    printf("\n");}int main(){    #ifdef LOCAL    freopen("in.txt","r",stdin);    #endif // LOCAL    int t;    scanf("%d",&t);    while(t--)    {        char s[maxn];        scanf("%s",s);        n = 0;        addnode(s);        BFS();    }    return 0;}

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