leetcode327. Count of Range Sum

Posted 2020-10-31 seyjs

题目如下：解题思路：本题是 560. Subarray Sum Equals K 的升级版，可以参见560的解题思路。唯一的区别是560只给了一个精确的和K，而本题是给了一个和的范围，所以最终计数的时候遍历一下题目要求的区间即可。

代码如下：

class Solution(object):
    def countRangeSum(self, nums, lower, upper):
        """
        :type nums: List[int]
        :type lower: int
        :type upper: int
        :rtype: int
        """
        if len(nums) == 0:
            return 0
        dp = [0 for x in nums]
        dp[-1] = nums[-1]

        keys = []
        dic = {}
        dic[dp[-1]] = 1
        keys.append(dp[-1])
        for i in xrange(-2, -len(nums) - 1, -1):
            dp[i] = dp[i + 1] + nums[i]
            if dic.has_key(dp[i]):
                dic[dp[i]] += 1
            else:
                dic[dp[i]] = 1
                keys.append(dp[i])
        res = 0
        keys.sort()
        print dic,dp
        for i, v in enumerate(dp):
            if v >= lower and v <= upper:
                res += 1
            dic[v] -= 1
            import bisect
            left = bisect.bisect_left(keys,v - upper)
            right = bisect.bisect_right(keys,v - lower)
            #print left,right,keys
            while left < right and left < len(keys):
                if dic.has_key(keys[left]):
                    res += dic[keys[left]]
                left += 1

        return res