solved 'Minimum Size Subarray Sum' on leetcode https://leetcode.com/problems/minimum-size-subarray-sum/

subarray_sum.cc

#include <cassert>
#include <climits>
#include <iostream>
#include <vector>

using namespace std;

// Inspired from
// https://leetcode.com/discuss/42143/4ms-solution-and-nlogn-solution-with-detailed-explanations
class Solution {
public:
  int minSubArrayLen(int s, vector<int>& nums) {
    int start = 0, res = INT_MAX, curr_sum = 0;
    for (int i = 0, len = nums.size(); i < len; ++i) {
      curr_sum += nums[i];
      while (curr_sum >= s) {
	res = min(res, i - start + 1);
	curr_sum -= nums[start++];
      }
    }
    return res == INT_MAX ? 0 : res;
  }
};

int main() {
  Solution sol;
  vector<int> nums;
  int res;

  nums = {1, 6};
  res = sol.minSubArrayLen(100, nums);
  assert(res == 0);

  nums = {1, 6};
  res = sol.minSubArrayLen(2, nums);
  assert(res == 1);

  nums = {1, 2, 3};
  res = sol.minSubArrayLen(6, nums);
  assert(res == 3);

  nums = {2, 3, 1, 2, 4, 3};
  res = sol.minSubArrayLen(7, nums);
  assert(res == 2); 
}

subarray_sum.py

class Solution:
    # @param {integer} s
    # @param {integer[]} nums
    # @return {integer}
    def minSubArrayLen(self, s, nums):
        prev, curr, nums_len = 0, 0, len(nums)
        # Accumulator to compare with s.
        acc = 0
        # Result.
        min_cnt = nums_len + 1
        while True:
            if acc < s:
                # End of story.
                if curr == nums_len:
                    break

                # Can only move forward `curr`.
                acc += nums[curr]
                curr += 1
            else:
                # Move `prev` forward until accumulator is 
                # smaller than s.
                while prev < curr and acc >= s:
                    acc -= nums[prev]
                    prev += 1
                # Compare with previous result.
                new_cnt = curr - prev + 1
                if new_cnt < min_cnt:
                    min_cnt = new_cnt

        return 0 if min_cnt == nums_len + 1 else min_cnt

if __name__ == '__main__':
    sol = Solution()

    nums, s = [1, 6], 2
    assert sol.minSubArrayLen(s, nums) == 1

    nums, s = [1, 2, 3], 6
    assert sol.minSubArrayLen(s, nums) == 3

    nums, s = [2, 3, 1, 2, 4, 3], 7
    assert sol.minSubArrayLen(s, nums) == 2