返回值遞歸問題

遇到此問題的時候，如果運行遞歸要返回值的話，一般可以這樣寫 return 后面接遞歸的函數。

題目一：數字在排序數組中出現的次數

class Solution {
public:
    int GetNumberOfK(vector<int> data ,int k) {
        int number=0;
        if(data.size()!=0){
            int first=GetFirstk(data,k,0,data.size()-1);
            int last=GetLastk(data,k,0,data.size()-1);
            if(first>-1&&last>-1)number=last-first+1;
        }
         
        return number;
    }
     
    int GetFirstk(vector<int>&data,int k,int start,int end){
        if(start>end)return -1;
        int mid=(start+end)>>1;
        if(data[mid]==k){
            if((mid>0&&data[mid-1]!=k)||mid==0)return mid;
            else
                return GetFirstk(data,k,start,mid-1);
        }
        else{
             if(data[mid]>k)return GetFirstk(data,k,start,mid-1);
             else
                return GetFirstk(data,k,mid+1,end);
        }
         
    }
     
    int GetLastk(vector<int>&data,int k,int start,int end){
        if(start>end)return -1;
        int mid=(start+end)>>1;
        if(data[mid]==k){
            if((mid<data.size()&&data[mid+1]!=k)||(mid==data.size()-1))return mid;
            else
                return GetLastk(data,k,mid+1,end);
        }
        else{
             if(data[mid]<k)return GetLastk(data,k,mid+1,end);
             else
                 return GetLastk(data,k,start,mid-1);
        }
         
    }
};

題目二：二叉樹的深度

class Solution {
public:
    int TreeDepth(TreeNode* pRoot)
    {
        if(!pRoot)return 0;
        return max(TreeDepth(pRoot->left),TreeDepth(pRoot->right))+1;
    
    }
};