1726.同积元组.js

/*
 * @lc app=leetcode.cn id=1726 lang=javascript
 *
 * [1726] 同积元组
 */

// @lc code=start
/**
 * @param {number[]} nums
 * @return {number}
 */
var tupleSameProduct = function(nums) {
  let tupleCount = 0;
  let products = {}; // we'll keep track of how many times we've seen a given product before
  for (let a = 0; a < nums.length; a++) {
      for (let b = a + 1; b < nums.length; b++) {        
          let product = nums[a] * nums[b];
          if (products[product]) { // we've seen at least one other pair of numbers with the same product already
              tupleCount += 8 * products[product]; // multiply by 8 because for any 4 numbers there are 8 permutations
              products[product] += 1; // increment the count, if we see this product again there are even more possible tuple combinations
          } else {
              products[product] = 1; // mark as seen once
          }
      }
  }
  return tupleCount;
};
// @lc code=end