Arithmetic Slices

A sequence of number is called arithmetic if it consists of at least three elements and if the difference between any two consecutive elements is the same.

For example, these are arithmetic sequence:

1, 3, 5, 7, 9
7, 7, 7, 7
3, -1, -5, -9

The following sequence is not arithmetic.

1, 1, 2, 5, 7

A zero-indexed array A consisting of N numbers is given. A slice of that array is any pair of integers (P, Q) such that 0 <= P < Q < N.

A slice (P, Q) of array A is called arithmetic if the sequence:
A[P], A[p + 1], …, A[Q - 1], A[Q] is arithmetic. In particular, this means that P + 1 < Q.

The function should return the number of arithmetic slices in the array A.

Example:

A = [1, 2, 3, 4]

return: 3, for 3 arithmetic slices in A: [1, 2, 3], [2, 3, 4] and [1, 2, 3, 4] itself.

"use strict";

/**
 * @param {number[]} A
 * @return {number}
 */
var numberOfArithmeticSlices = function(A) {
  let len = A.length;
  let ans = 0;

  for (let i = 0; i < len; i++) {
    let diff;
    let num = 2;
    for (let j = i + 1; j < len; j++) {
      if (j === i + 1)
        diff = A[j] - A[i];
      else if (A[j] - A[j - 1] === diff)
        num++;
      else
        break;
    }

    ans += num - 2;
  }

  return ans;
};

Arranging Coins

You have a total of n coins that you want to form in a staircase shape, where every k-th row must have exactly k coins.

Given n, find the total number of full staircase rows that can be formed.

n is a non-negative integer and fits within the range of a 32-bit signed integer.

Example 1:

n = 5

The coins can form the following rows:
¤
¤ ¤
¤ ¤

Because the 3rd row is incomplete, we return 2.

Example 2:

n = 8

The coins can form the following rows:
¤
¤ ¤
¤ ¤ ¤
¤ ¤

Because the 4th row is incomplete, we return 3.

"use strict";

/**
 * @param {number} n
 * @return {number}
 */
var arrangeCoins = function(n) {
  let ans = Math.sqrt(1 + 8 * n) - 1;
  ans /= 2;

  return ~~ans;
};

Assign Cookies

Assume you are an awesome parent and want to give your children some cookies. But, you should give each child at most one cookie. Each child $i$ has a greed factor $g_i$, which is the minimum size of a cookie that the child will be content with; and each cookie $j$ has a size $s_j$. If $s_j >= g_i$, we can assign the cookie $j$ to the child $i$, and the child $i$ will be content. Your goal is to maximize the number of your content children and output the maximum number.

Note:

You may assume the greed factor is always positive.

You cannot assign more than one cookie to one child.

Example 1:

Input: [1,2,3], [1,1]

Output: 1

Explanation: You have 3 children and 2 cookies. The greed factors of 3 children are 1, 2, 3. 
And even though you have 2 cookies, since their size is both 1, you could only make the child whose greed factor is 1 content.
You need to output 1.

Example 2:

Input: [1,2], [1,2,3]

Output: 2

Explanation: You have 2 children and 3 cookies. The greed factors of 2 children are 1, 2. 
You have 3 cookies and their sizes are big enough to gratify all of the children, 
You need to output 2.

/**
 * @param {number[]} g
 * @param {number[]} s
 * @return {number}
 */
var findContentChildren = function(g, s) {
  g.sort(function(a, b) {return a - b;});
  s.sort(function(a, b) {return a - b;});

  let ans = 0;
  let sIndex = 0;
  let sLen = s.length;

  // greedy
  loop:
  for (let i = 0, len = g.length; i < len; i++) {
    let item = g[i];

    for (let j = sIndex; j < sLen; j++) {
      if (s[j] >= item) {
        ans++;
        sIndex = j + 1; // the index next loop should be from
        if (sIndex === sLen) break loop;
        break;
      }
    }
  }

  return ans;
};