Random pick with weight

Author: ramanaditya

leetcode/README.md

@@ -87,6 +87,7 @@
     | 240. | <span style="color:orange">Medium</span> | [Search a 2D Matrix II](https://leetcode.com/problems/search-a-2d-matrix-ii/) | [Python](https://github.com/ramanaditya/data-structure-and-algorithms/blob/master/leetcode/binary-search/search-a-2d-matrix-ii.py) |
     | 278. | <span style="color:green">Easy</span> | [278. First Bad Version](https://leetcode.com/problems/first-bad-version/) | [Python](https://github.com/ramanaditya/data-structure-and-algorithms/blob/master/leetcode/binary-search/first-bad-version.py) |
     | 367. | <span style="color:green">Easy</span> | [Valid Perfect Square](https://leetcode.com/problems/valid-perfect-square/) | [Python](https://github.com/ramanaditya/data-structure-and-algorithms/blob/master/leetcode/binary-search/valid-perfect-square.py) |
+    | 528. | <span style="color:orange">Medium</span> | [Random Pick with Weight](https://leetcode.com/problems/random-pick-with-weight/) | [Python](https://github.com/ramanaditya/data-structure-and-algorithms/blob/master/leetcode/binary-search/random-pick-with-weight.py) |
     | 540. | <span style="color:orange">Medium</span> | [Single Element in a Sorted Array](https://leetcode.com/problems/single-element-in-a-sorted-array/) | [Python](https://github.com/ramanaditya/data-structure-and-algorithms/blob/master/leetcode/binary-search/single-element-in-a-sorted-array.py) |
     | 704. | <span style="color:green">Easy</span> |[Binary Search](https://leetcode.com/problems/binary-search/) | [Python](https://github.com/ramanaditya/data-structure-and-algorithms/blob/master/leetcode/binary-search/binary-search.py) |
     | 1198. | <span style="color:orange">Medium</span> | [Find Smallest Common Element in All Rows](https://leetcode.com/problems/find-smallest-common-element-in-all-rows/) | [Python](https://github.com/ramanaditya/data-structure-and-algorithms/blob/master/leetcode/binary-search/find-smallest-common-element-in-all-rows.py) |
@@ -307,4 +308,4 @@
     | 2 | 237. | <span style="color:green">Easy</span> | [Delete Node in a Linked List](https://leetcode.com/problems/delete-node-in-a-linked-list/) | [Python](https://github.com/ramanaditya/data-structure-and-algorithms/tree/master/leetcode/linked-list/delete-node-in-a-linked-list.py) \| [C++](https://github.com/ramanaditya/data-structure-and-algorithms/tree/master/leetcode/linked-list/delete-node-in-a-linked-list.cpp) |
     | 3 | 1029. | <span style="color:green">Easy</span> | [Two City Scheduling](https://leetcode.com/problems/two-city-scheduling/) | [Python](https://github.com/ramanaditya/data-structure-and-algorithms/blob/master/leetcode/greedy/two-city-scheduling.py) | 
     | 4 | 344. | <span style="color:green">Easy</span> | [Revese String](https://leetcode.com/problems/reverse-string/) | [Python](https://github.com/ramanaditya/data-structure-and-algorithms/blob/master/leetcode/array/reverse-string.py) |
-    
+    | 5 | 528. | <span style="color:orange">Medium</span> | [Random Pick with Weight](https://leetcode.com/problems/random-pick-with-weight/) | [Python](https://github.com/ramanaditya/data-structure-and-algorithms/blob/master/leetcode/binary-search/random-pick-with-weight.py) |

leetcode/binary-search/random-pick-with-weight.py

@@ -0,0 +1,52 @@
+"""
+Medium
+## Questions
+### [528. Random Pick with Weight](https://leetcode.com/problems/random-pick-with-weight/)
+
+Given an array w of positive integers, where w[i] describes the weight of index i, write a function pickIndex which
+randomly picks an index in proportion to its weight.
+
+Note:
+1 <= w.length <= 10000
+1 <= w[i] <= 10^5
+pickIndex will be called at most 10000 times.
+
+Example 1:
+Input:
+["Solution","pickIndex"]
+[[[1]],[]]
+Output: [null,0]
+
+Example 2:
+Input:
+["Solution","pickIndex","pickIndex","pickIndex","pickIndex","pickIndex"]
+[[[1,3]],[],[],[],[],[]]
+Output: [null,0,1,1,1,0]
+
+Explanation of Input Syntax:
+The input is two lists: the subroutines called and their arguments. Solution's constructor has one argument,
+the array w. pickIndex has no arguments. Arguments are always wrapped with a list, even if there aren't any.
+"""
+
+
+# Solutions
+
+
+class Solution:
+    def __init__(self, w: List[int]):
+        self.prefix_sum = list(itertools.accumulate(w))
+
+    def pickIndex(self) -> int:
+        if not self.prefix_sum:
+            return 0
+        rand = random.randint(0, self.prefix_sum[-1] - 1)
+        return bisect.bisect_right(self.prefix_sum, rand)
+
+
+# Your Solution object will be instantiated and called as such:
+# obj = Solution(w)
+# param_1 = obj.pickIndex()
+
+
+# Runtime: 232 ms, faster than 91.15% of Python3 online submissions
+# Memory Usage: 18.2 MB, less than 81.65% of Python3 online submissions