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Given an array of n positive integers and a positive integer s, find the minimal length of a subarray of which the sum ≥ s. If there isn‘t one, return -1 instead.
Given the array [2,3,1,2,4,3] and s = 7, the subarray [4,3] has the minimal length under the problem constraint.
If you have figured out the O(n) solution, try coding another solution of which the time complexity is O(n log n).
Analyse: Two pointers. O(n)
Runtime: 203ms
1 class Solution { 2 public: 3 /** 4 * @param nums: a vector of integers 5 * @param s: an integer 6 * @return: an integer representing the minimum size of subarray 7 */ 8 int minimumSize(vector<int> &nums, int s) { 9 // write your code here 10 // mark left, set right as left + 1 11 // move right until sum of nums[left...right] >= s 12 // update the min length and let left move one position 13 // if current sum >= s update min length and keep move left 14 // if current sum < s move right one position 15 16 if (nums.empty()) return -1; 17 int left = 0, right = 1; 18 int minSize = INT_MAX, tempSum = nums[left]; 19 if (tempSum > s) return 1; 20 while (left < nums.size() && right < nums.size()) { 21 tempSum += nums[right]; 22 while (tempSum >= s) { 23 minSize = min(minSize, right - left + 1); 24 tempSum -= nums[left]; 25 left++; 26 } 27 if (tempSum < s) { 28 right++; 29 } 30 } 31 return minSize == INT_MAX ? -1 : minSize; 32 } 33 };
Analyse: Brute force. O(n^2)
Runtime: 605ms
1 class Solution { 2 public: 3 /** 4 * @param nums: a vector of integers 5 * @param s: an integer 6 * @return: an integer representing the minimum size of subarray 7 */ 8 int minimumSize(vector<int> &nums, int s) { 9 // write your code here 10 if (nums.empty()) return -1; 11 12 int result = INT_MAX; 13 for (int i = 0; i < nums.size(); i++) { 14 int tempSum = nums[i]; 15 if (tempSum >= s) return 1; 16 for (int j = i + 1; j < nums.size(); j++) { 17 tempSum += nums[j]; 18 if (tempSum >= s) { 19 result = min(result, j - i + 1); 20 break; 21 } 22 } 23 } 24 return result == INT_MAX ? -1 : result; 25 } 26 };
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原文地址：http://www.cnblogs.com/amazingzoe/p/5820400.html
