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class { public int addDigits(int num) { if(num < 10)return num; int res = 0; while(num>0){ res+=num%10; num/=10; } return addDigits(res); } }
- X = f(abc) - X = 100*a+10*b+c - X = 99*a+9*b+a+b+c - X = 9*(11*a+b)+a+b+c - X = abc%9 = a+b+c class { public int addDigits(int num){ return (num-1)%9+1; } }
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