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FindMissingNum.java
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49 lines (39 loc) · 1018 Bytes
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package array_practice;
public class FindMissingNum {
public static void printArray(int[] arr) {
int n = arr.length;
for(int i = 0; i < n; i++ ) {
System.out.print(arr[i] + " ");
}
System.out.println();
}
// 1st approach
// public static int findMissingNum(int[] arr) {
// int n = arr.length + 1;
// //formula for sum of first n natural nums: n(n+1)/2
// int formulaSum = n*(n+1)/2;
// int arrSum = 0;
// for(int i = 0; i<n-1 ; i++) {
//// System.out.println(arrSum + arr[i] );
// arrSum += arr[i];
// }
// int num = formulaSum - arrSum;
// return num;
//
//
// }
public int findMissingNum(int[] arr) {
int n = arr.length + 1;
int formulaSum = n*(n+1)/2;
for(int i = 0; i<n-1 ; i++) {
formulaSum = formulaSum - arr[i];
}
return formulaSum;
}
public static void main(String[] args) {
FindMissingNum findNum = new FindMissingNum();
int[] arr = {1,2,5,4};
printArray(arr);
System.out.println("missign num: "+ findNum.findMissingNum(arr));
}
}