274. H-Index.js

/*Given an array of citations (each citation is a non-negative integer) of a researcher, write a function to compute the researcher's h-index.

According to the definition of h-index on Wikipedia: "A scientist has index h if h of his/her N papers have at least h citations each, and the other N − h papers have no more than h citations each."

Example:

Input: citations = [3,0,6,1,5]
Output: 3 
Explanation: [3,0,6,1,5] means the researcher has 5 papers in total and each of them had 
             received 3, 0, 6, 1, 5 citations respectively. 
             Since the researcher has 3 papers with at least 3 citations each and the remaining 
             two with no more than 3 citations each, her h-index is 3.
Note: If there are several possible values for h, the maximum one is taken as the h-index.*/

/**
 * @param {number[]} citations
 * @return {number}
 */
var hIndex = function(citations) {
  let i = -1, len = citations.length
  if (len === 0) return 0
  if (len === 1) return citations[0] === 0 ? 0 : 1
  citations.sort((a, b) => b - a)
  while (++i < len) {
    if (i + 1 > citations[i]) return i
  }
  return len
};






var hIndex = function(citations) {
  let len = citations.length, count = []
  for (let i = 0; i <= len; i++) {
    count.push(0)
  }

  for (let i = 0; i < len; i++) {
    let ci = citations[i]
    if (ci >= len) count[len] = count[len] + 1
      else count[ci] = count[ci] + 1
  }

  for (let i = len - 1; i >= 0; i--) {
    count[i] = count[i] + count[i + 1]
  }

  for (let i = len; i >= 0; i--) {
    if (count[i] >= i) return i
  }
};