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How can I find the missing number in an array with an integer between 1 and 100?

Here's what I did. What can I do next? Can anyone suggest? I am looking for a bitt solution.

public static void main(String args[]) {

// one missing number
printMissingNumber(new int[]{1, 2, 3, 4, 6}, 6);

// two missing number
printMissingNumber(new int[]{1, 2, 3, 4, 6, 7, 9, 8, 10}, 10);

// three missing number
printMissingNumber(new int[]{1, 2, 3, 4, 6, 9, 8}, 10);

// four missing number
printMissingNumber(new int[]{1, 2, 3, 4, 9, 8}, 10);

 // Only one missing number in array
int[] iArray = new int[]{1, 2, 3, 5};
int missing = getMissingNumber(iArray, 5);
System.out.printf("Missing number in array %s is %d %n", 
Arrays.toString(iArray), missing);

}

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2 answers


For n consecutive numbers, the sum s = n (n + 1) / 2.



Sum the numbers in the array and subtract them from s to find the missing number.

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If n

is the largest number, and only one is missing, then the missing number

n * (n + 1) / 2 - sum{elements in your array}


The first term is the sum of n

consecutive integers from 1 to including n

.

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