leetcode 209. Minimum Size Subarray Sum (尺取法)

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

思路：尺取即可。。好久没写，竟然调了半天。。。

/* ***********************************************
Author :111qqz
Created Time :2017年04月13日 星期四 20时48分00秒
File Name :209.cpp
************************************************ */
class Solution {

public:

	int ruler(vector<int>nums,int tar,int n)
	{
	    int head = 0;
	    int tail = 0;
	    int sum = 0 ;
	    int res = 0x3f3f3f3f;
	    while (tail<n&&head<=tail)
	    {
		sum = sum + nums[tail];
		if (sum>=tar)
		{
		    res = min(res,tail-head+1);
		    while (sum>=tar&&head<tail)
		    {
			sum-=nums[head];
			head++;
		    }
		    if (sum>=tar) 
		    {
			res = min(res,tail-head+1);
		    }
		    else
		    {
			head--;
			sum+=nums[head];
			res = min(res,tail-head+1);
		    }
		}



		tail++;
	    }
	    return res==0x3f3f3f3f?0:res;
	}


    int minSubArrayLen(int s, vector<int>& nums) {
	int n = nums.size();
	int res = ruler(nums,s,n);
	return res;
        

    }

};