分析:矩阵每一行,计算prefix sum,然后对于任意两列,计算行的累加和,问题就转换为了Subarray Sum Equals K time O(n3n3) space O(n) classSolution {public:intnumSubmatrixSumTarget(vector<vector<int>>& matrix,inttarget) {intm = matrix.size(), n = matrix[0].size();for(inti =0; i < m; ++i...
无独有偶,leetcode最近的contest中出了一题非常类似的问题,本质上依然是最长target sum的子数组,当时的想法也是陷入了范式中,错误的认为子数组的问题都可以使用dp或者滑动数组进行求解,导致走入了死胡同。 本题也是一条变种题,可见如何直接出subarray of target sum 是没有多大的价值的,这个题目直接问的话,就非常简...
本题也是一条变种题,可见如何直接出subarray of target sum 是没有多大的价值的,这个题目直接问的话,就非常简单直白,很容易就会想到使用hashmap去求解,但是如果进行一下包装,就未必能想到了。 总之,碰到subarray的问题,不仅要能联想到dp/sliding window,还要有意识去想想其他的解法。 publicintlongestWPI(int[]hours...
Given a binary array, find the maximum length of a contiguous subarray with equal number of 0 and 1. 这里我们所关心的状态其实是0和1出现个数的差异。如果A[0 .. i] 中0和1出现个数差异与A[0 .. j]中0和1出现个数差异相等的话,那么A[i+1 .. j]中0和1的个数应当相等(assume i < j)...
class Solution { public: int maxNonOverlapping(vector<int>& nums, int target) { unordered_map<int,int> map; map[0]=1; int cnt=0; int sum=0; for(auto& x: nums){ sum+=x; if(map.count(sum-target)){ cnt++; map.clear(); map[0]=1; sum=0; } else{ map[sum]++; } } retu...
2.Smallest Subarray with a given sum(easy) 2.1 问题描述 Given an array of positive integers nums and a positive integer target, return the minimal length of a 「contiguous subarray」 [numsl, numsl+1, ..., numsr-1, numsr] of which the sum is greater than or equal to target. If th...
prefix sum//save the prefix sum to a hashset//every time we get a target, we check for each number x in the//hashset, if tartget + k exists//in the case of two prefix with same val, use two hashset. save the second to dup setpublicbooleansubarraySum(int[] array,inttarget){ ...
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Leetcode之Minimum Path Sum 问题 问题描述: Given a m x n grid filled with non-negative numbers, find a path from top left to bottom right whichminimizes the sum of all numbers along its path. Note: You can only move either down or right ... ...
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