> For the complete documentation index, see [llms.txt](https://juneglee.gitbook.io/til/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://juneglee.gitbook.io/til/algorithm/recursion.md).

# recursion

## recursion

## 재귀를 이용한 한자릿수 만들기

```java
// input 자연수 n이 주어졌을 때
// ex1) 10 일 경우 1 + 0 => 1
// ex2) 456789 일 경우 4 + 5 + 6 + 7 + 8 + 9 => 39
//                     39 = > 3 + 9 = > 12 
//                     12 = > 1 + 2 => 3
public class recursion {
    public static int compute(int source) {
        if (source < 10) {
            return source;
        }

        String sourceStr = Integer.toString(source);

        int sum = 0;
        for (int i = 0 ; i < sourceStr.length(); i ++) {
            char ch = sourceStr.charAt(i);
            int num = (int) ch - 48; // 아스키 코드
            sum +=num;
        }
        return compute(sum); // 재귀 호출 
    }

    public static void main(String[] args) {
        int num = compute(456789);
        System.out.println(num); // 3
    }
}
```


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