{"id":4971,"date":"2019-03-11T23:20:17","date_gmt":"2019-03-12T06:20:17","guid":{"rendered":"https:\/\/zxi.mytechroad.com\/blog\/?p=4971"},"modified":"2019-03-11T23:20:19","modified_gmt":"2019-03-12T06:20:19","slug":"leetcode-930-binary-subarrays-with-sum","status":"publish","type":"post","link":"https:\/\/zxi.mytechroad.com\/blog\/algorithms\/array\/leetcode-930-binary-subarrays-with-sum\/","title":{"rendered":"LeetCode 930. Binary Subarrays With Sum"},"content":{"rendered":"\n<p>In an array&nbsp;<code>A<\/code>&nbsp;of&nbsp;<code>0<\/code>s and&nbsp;<code>1<\/code>s, how many&nbsp;<strong>non-empty<\/strong>&nbsp;subarrays have sum&nbsp;<code>S<\/code>?<\/p>\n\n\n\n<p><strong>Example 1:<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-preformatted crayon:false\"><strong>Input: <\/strong>A = [1,0,1,0,1], S = 2\n<strong>Output: <\/strong>4\n<strong>Explanation: <\/strong>\nThe 4 subarrays are bolded below:\n[<strong>1,0,1<\/strong>,0,1]\n[<strong>1,0,1,0<\/strong>,1]\n[1,<strong>0,1,0,1<\/strong>]\n[1,0,<strong>1,0,1<\/strong>]\n<\/pre>\n\n\n\n<p><strong>Note:<\/strong><\/p>\n\n\n\n<ol class=\"wp-block-list\"><li><code>A.length &lt;= 30000<\/code><\/li><li><code>0 &lt;= S &lt;= A.length<\/code><\/li><li><code>A[i]<\/code>&nbsp;is either&nbsp;<code>0<\/code>&nbsp;or&nbsp;<code>1<\/code>.<\/li><\/ol>\n\n\n\n<h2 class=\"wp-block-heading\"><strong>Solution: Prefix Sum<\/strong><\/h2>\n\n\n\n<p>counts[s] := # of subarrays start from 0 that have sum of s<br>ans += counts[s &#8211; S] if s &gt;= S<\/p>\n\n\n\n<p>Time complexity: O(n)<br>Space complexity: O(n)<\/p>\n\n\n\n<div class=\"responsive-tabs\">\n<h2 class=\"tabtitle\">C++<\/h2>\n<div class=\"tabcontent\">\n\n<pre lang=\"c++\">\n\/\/ Author: Huahua, 28 ms, 12.3 MB\nclass Solution {\npublic:\n  int numSubarraysWithSum(vector<int>& A, int S) {\n    const int n = A.size();\n    vector<int> counts(n + 1);\n    counts[0] = 1;\n    int ans = 0;\n    int sum = 0;\n    for (int a : A) {\n      sum += a;      \n      if (sum >= S) ans += counts[sum - S];\n      ++counts[sum];\n    }\n    return ans;\n  }\n};\n<\/pre>\n<\/div><\/div>\n","protected":false},"excerpt":{"rendered":"<p>In an array&nbsp;A&nbsp;of&nbsp;0s and&nbsp;1s, how many&nbsp;non-empty&nbsp;subarrays have sum&nbsp;S? Example 1: Input: A = [1,0,1,0,1], S = 2 Output: 4 Explanation: The 4 subarrays are bolded&#8230;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[184],"tags":[20,177,200],"class_list":["post-4971","post","type-post","status-publish","format-standard","hentry","category-array","tag-array","tag-medium","tag-prefix-sum","entry","simple"],"_links":{"self":[{"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/posts\/4971","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/comments?post=4971"}],"version-history":[{"count":1,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/posts\/4971\/revisions"}],"predecessor-version":[{"id":4972,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/posts\/4971\/revisions\/4972"}],"wp:attachment":[{"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/media?parent=4971"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/categories?post=4971"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/tags?post=4971"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}