[Jianzhi offer] 64 Find 1+2+... +n

The finger of the sword Offer 64. seek 1+2+…+n

subject

  seek 1+2+…+n , It is required that multiplication and division shall not be used 、for、while、if、else、switch、case Wait for keywords and conditional statements （A?B:C）.

Ideas

• take if The judgment statement is converted into the method of short-circuit evaluation .
• Short circuit evaluation ：if(A & &B) // If A yes True, Then keep watching B,A yes False, There is no need to see B;if(A || B) // If A yes True, Then there's no need to see B, If A yes Flase, Still have to see B.
• First write the ordinary recursive form , In the form of short-circuit evaluation

Code

• Short circuit evaluation

class Solution {
    
public:
    int sumNums(int n) {
    
        bool x = n > 1 && (n += sumNums(n - 1)) > 0;
        return n;
    }
};

• Recursive form

class Solution {
    
public:
    int sumNums(int n) {
    
      if(n == 1) return 1;
    n += sumNums(n - 1);
    return n;
    }
};