通过Java中的Eratosthenes筛子求和：仅当参数为质数时失败

Question

My implementation of the sieve itself seems to be working fine, and the summing function returns the correct result as long as the last value is not itself a prime number. Oddly, I can see the primality is duly noted in the true/false array if I return it directly, but I can't seem to actually get at it for the purposes of summing. As a result, running this Sieve on 10 returns 17 (correct), but running it on 37 returns 160 instead of 197. Running it on 5 returns 5 instead of 10, and so forth.

function sumPrimes(n) {
  var primArr = [];
  var primSum = 0;
  for (var i = 2; i < n; i++) {
    primArr[i] = true;
  }

  //sieve

  for (i = 2; i * i < n; i++) {
    if (primArr[i]){
      for (var j = 0; i * i + i * j < n; j++) {
        primArr[i * i + i * j] = false;
      }
    }
  }

  for (i = 2; i <= n; i++) {
    if (primArr[i]) {
      primSum += i;
    }
  }

  return primSum;
}

Answer 1

In all your for loops put the condition <= n , since you want to consider n itself as well.

Note that you save some calculations if you change the middle part to this:

for (var i = 2, sqrtN = Math.sqrt(n); i <= sqrtN; i++) {
    if (primArr[i]){
        for (var j = i * i; j <= n; j += i) {
            primArr[j] = false;
        }
    }
}