Maximum Running Time of N Computers LeetCode solution in Java

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class Solution {
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  private boolean canFit(int n, long k, int[] batteries) {
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    long currBatSum = 0;
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    long target = n * k;
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    for (int bat : batteries) {
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      if (bat < k) {
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        currBatSum += bat;
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      } else {
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        currBatSum += k;
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      }
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      if (currBatSum >= target) {
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        return true;
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      }
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    }
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    return currBatSum >= target;
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  }
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  public long maxRunTime(int n, int[] batteries) {
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    long batSum = 0;
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    for (int bat : batteries) {
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      batSum += bat;
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    }
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    long lower = 0;
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    long upper = batSum / n;
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    long res = -1;
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    // binary search
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    while (lower <= upper) {
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      long mid = lower + (upper - lower) / 2;
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      if (canFit(n, mid, batteries)) {
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        res = mid;
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        lower = mid + 1;
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      } else {
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        upper = mid - 1;
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      }
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    }
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    return res;
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  }
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}