LeetCode 209. Minimum Size Subarray Sum

Given an array of n positive integers and a positive integer s, find the minimal length of a contiguous subarray of which the sum ≥ s.
If there isn't one, return 0 instead.

For example, given the array 

[2,3,1,2,4,3]

 and 

s
= 7

,

the subarray 

[4,3]

 has the minimal length under the problem constraint.

click to show more practice.

More practice:
If you have figured out the O(n) solution, try coding another solution of which the time complexity is O(n log n).

分析：

运用前缀和，i到j之间的和为sum[j]-sum[i]+nums[i]，如果大于等于s，则与minn比较，求最小值

class Solution {
public:
int minSubArrayLen(int s, vector<int>& nums) {

int minn=100000008;
int sum[nums.size()+1];
for(int i=0;i<nums.size();i++){
if(nums[i]>=s) return 1;
if(i==0) sum[i]=nums[i];
else sum[i]=sum[i-1]+nums[i];
}
for(int i=0;i<nums.size();i++){
for(int j=i+1;j<nums.size();j++){
if(sum[j]-sum[i]+nums[i]>=s){
minn=min(j-i+1,minn);
if(minn==2) return 2;
break;
}
}
}
if(minn==100000008) return 0;
else return minn;
}
};