Find ith largest array in an array

Question:

　　Given an integer array, find out the second largest item.

Analysis:

　　Sort the array (ascending) first. The second largest will be the last but one? Too young, too simple, sometimes naive. It will not work if there are duplicated times. E.g. [2,5,8,3,8,7].

　　We can use two indicators, li (largest item index, set to 0 initially) and slii (second largest item index, set to -1 initially). Traverse the array, starting from the second item in the array, let lii store the largest item‘s index, slii store the second largest one‘s. It can complete in O(n).

Code:

   public static int findSecondLargest(final int[] array) {
      if (array != null && array.length >= 2) {
         int lii = 0;
         int slii = -1;

         for (int i = 1; i < array.length; i++) {
            if (array[i] > array[lii]) {
               slii = lii;
               lii = i;
            } else if (array[i] == array[lii]) {
               continue;
            } else {
               slii = (slii == -1 || array[slii] < array[i]) ? i : slii;
            }

         return slii;
      }

      return -1;
   }

　　So far so good.

Question:

　　Given an integer array, find out the third largest item.

Analysis:

　　WTH? Use three indicators, lii, slii, tlii (third largest item index).

public static int findThirdLargest(final int[] array) {
      if (array != null && array.length >= 3) {
         int lii = 0;
         int slii = -1;
         int tlii = -1;

         for (int i = 1; i < array.length; i++) {
            if (array[i] > array[lii]) {
               tlii = slii;
               slii = lii;
               lii = i;
            } else if (array[i] == array[lii]) {
               continue;
            } else {
               if (slii == -1) {
                  slii = i;
               } else {
                  if (array[i] > array[slii]) {
                     tlii = slii;
                     slii = i;
                  } else if (array[i] == array[slii]) {
                     continue;
                  } else {
                     tlii = (tlii == -1 || array[tlii] < array[i]) ? i : tlii;
                  }
               }
            }
         }

         return tlii;
      }

      return -1;
   }

　　It smells. I‘m kind of repeating myself.

Question:

　　Given an integer array, find out the ith largest item.

Analysis:

　　WTF? Use i indicators? Write i methods? Don‘t repeat yourself (DRY). To find out the ith largest item, we use an assistant array indicators.

public static int findithLargest(final int ith, final int[] array) {
      if (array == null || ith < 1 || array.length < ith) {
         return -1;
      }

      int[] inidcators = new int[ith];
      for (int i = 1; i < ith; i++) {
         inidcators[i] = -1;
      }

      for (int i = 1; i < array.length; i++) {
         updateIndices(i, array, 0, inidcators);
      }

      return inidcators[ith - 1];
   }

   private static void updateIndices(final int cur, final int[] array, final int ithlii, int[] inidcators) {
      if (ithlii < inidcators.length) {
         if (inidcators[ithlii] == -1) {
            inidcators[ithlii] = cur;
         } else if (array[cur] > array[inidcators[ithlii]]) {
            for (int i = inidcators.length - 1; i > ithlii; i--) {
               inidcators[i] = inidcators[i - 1];
            }
            inidcators[ithlii] = cur;
         } else if (array[cur] == array[inidcators[ithlii]]) {
            return;
         } else {
            updateIndices(cur, array, ithlii + 1, inidcators);
         }
      }
   }