hdu 1805 Expressions (建树与层序遍历)

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#include <iostream>#include <stdlib.h>#include <stack>#include <string.h>#include <queue>#define maxn 100101using namespace std;int flag;typedef struct BiNode{    char value;    struct BiNode *left,*right;} BiNode,*BiTree;int main(){    int n,cnt;    char str[maxn];    char ans[maxn];    stack<BiTree>s;    cin>>n;    while(n--)    {        cin>>str;        int len = strlen(str);        for(int i = 0; i < len; i++)        {            if(str[i]>='a'&&str[i]<='z')            {                BiTree u=(BiTree)malloc(sizeof(BiNode));                u->value=str[i];                u->left=u->right=NULL;                s.push(u);            }            else if(str[i]>='A'&&str[i]<='Z')            {                BiTree x,y;                x=s.top();                s.pop();                y=s.top();                s.pop();                BiTree u=(BiTree)malloc(sizeof(BiNode));                u->value=str[i];                u->left=y;                u->right=x;                s.push(u);            }        }        BiTree u=s.top();        queue<BiTree>q;        cnt=0;        q.push(u);        while(!q.empty())        {            BiTree v=q.front();            q.pop();            ans[cnt++]=v->value;            if(v->left)q.push(v->left);            if(v->right)q.push(v->right);        }        for(int i=cnt-1; i>=0; i--)            cout<<ans[i];        cout<<endl;        while(!s.empty())s.pop();    }    return 0;}

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