二叉树递归算法：
1．统计二叉树中，度为0的结点个数
2．统计二叉树中，度为1的结点个数
3．统计二叉树中，度为2的结点个数
4．统计二叉树高度
5．统计二叉树宽度
6．删除二叉树中所有叶子节点
7．交换每个节点的左右子女

#include <stdio.h>
#include <stdlib.h>
int s[20]={0};
typedef struct BiTNode{
    char data;
    struct BiTNode *lchild,*rchild;
}BiTNode,*BiTree;

BiTree CreateBiTree( ){
    char ch;
    scanf("%c",&ch);
    if(ch=='#') return NULL;
    else{
        BiTree T = (BiTree)malloc(sizeof(BiTNode));
        T -> lchild  = T -> rchild = NULL;
        T->data = ch;
        T->lchild = CreateBiTree();
        T->rchild = CreateBiTree();
        return T;
    }

}
//统计二叉树中度为0的结点个数
int Degree_0(BiTree T){
    if(T==NULL) return 0 ;
    if( T->lchild==NULL && T->rchild == NULL )
        return 1 + Degree_0(T->lchild )+ Degree_0(T->rchild) ;
    else
        return Degree_0(T->lchild )+ Degree_0(T->rchild) ;
}
//统计二叉树中度为1的结点个数
int Degree_1(BiTree T){
    if(T==NULL) return 0 ;
    if(( T->lchild!=NULL && T->rchild == NULL ) ||( T->lchild==NULL && T->rchild != NULL ) )
        return 1 + Degree_1(T->lchild )+ Degree_1(T->rchild) ;
    else
        return Degree_1(T->lchild )+ Degree_1(T->rchild) ;
}
//统计二叉树中度为2的结点个数
int Degree_2(BiTree T){
    if(T==NULL) return 0 ;
    if( T->lchild!=NULL && T->rchild != NULL )
        return 1 + Degree_2(T->lchild )+ Degree_2(T->rchild) ;
    else
        return Degree_2(T->lchild )+ Degree_2(T->rchild) ;
}
//统计二叉树高度
int Depth( BiTree T ){
    int ldept , rdept ;
    if(T == NULL) return 0;
    else{
        ldept = Depth(T->lchild);
        rdept = Depth(T->rchild);
        return (ldept>rdept?ldept:rdept)+1;
    }
}
//统计二叉树宽度
void Width( BiTree T ,int deep){
    if(T == NULL) return ;
    else{
        s[deep]++ ;
        Width( T->lchild , deep +1 );
        Width( T->rchild , deep +1 );
    }
}
//交换二叉树中左右子女
void swap(BiTree T){
    BiTNode *p ;
    if(T){
        swap(T->lchild);
        swap(T->rchild);
        p = T->lchild ;
        T->lchild = T->rchild ;
        T->rchild = p ;
    }
}
//删除二叉树所有叶节点
void Delete_leaves(BiTree T){
    if( T ){
        if(T->lchild){
            if(T->lchild->lchild==NULL&&T->lchild->rchild==NULL){
                free(T->lchild);
                T->lchild=NULL ;
            }
            else
                Delete_leaves(T->lchild);
        }
        if(T->rchild){
            if(T->rchild->lchild==NULL&&T->rchild->rchild==NULL){
                free(T->rchild);
                T->rchild=NULL ;
            }
            else
                Delete_leaves(T->rchild);

        }
    }
}

void PreOrderTraverse(BiTree T){
    if(T){
        printf("%c",T->data);
        PreOrderTraverse(T->lchild);
        PreOrderTraverse(T->rchild);
    }
}

int main(){
    printf("输入各节点：\n");
    BiTree T = CreateBiTree();
    printf("度为0的结点个数：%d \n",Degree_0(T));
    printf("度为1的结点个数：%d \n",Degree_1(T));
    printf("度为2的结点个数：%d \n",Degree_2(T));
    printf("二叉树高度:%d \n",Depth(T));
    Width(T,0);
    int max=0;
    for(int i=0;s[i]!=0;i++)
    {
        if(s[i]>max)
        max=s[i];
    }
    printf("二叉树宽度:%d \n",max);
    printf("交换二叉树左右子树:");
    PreOrderTraverse(T);printf("\n");
    Delete_leaves(T);
    printf("删除叶子节点:");
    PreOrderTraverse(T);
    printf("\n");
    swap(T);
}