From 4f774dbdfae7dfca4f161d98e2708ff096e33b4c Mon Sep 17 00:00:00 2001
From: Hieu Luong <hieu.luong.dinh.ext@proximus.com>
Date: Wed, 29 Jul 2020 15:04:40 +0200
Subject: [PATCH] Solve Problem 1508 - Range Sum Of Sorted Subarray Sums

---
 src/Main.java                                 |  4 +-
 ...blem1508_RangeSumOfSortedSubarraySums.java | 56 +++++++++++++++++++
 2 files changed, 58 insertions(+), 2 deletions(-)
 create mode 100644 src/binarysearch/Problem1508_RangeSumOfSortedSubarraySums.java

diff --git a/src/Main.java b/src/Main.java
index a617bfb..c0c7a64 100644
--- a/src/Main.java
+++ b/src/Main.java
@@ -1,8 +1,8 @@
-import quickselect.Problem347_TopKFrequentElements;
+import binarysearch.Problem1508_RangeSumOfSortedSubarraySums;
 
 public class Main {
 
     public static void main(String[] args) {
-        Problem347_TopKFrequentElements.run();
+        Problem1508_RangeSumOfSortedSubarraySums.run();
     }
 }
diff --git a/src/binarysearch/Problem1508_RangeSumOfSortedSubarraySums.java b/src/binarysearch/Problem1508_RangeSumOfSortedSubarraySums.java
new file mode 100644
index 0000000..8931c72
--- /dev/null
+++ b/src/binarysearch/Problem1508_RangeSumOfSortedSubarraySums.java
@@ -0,0 +1,56 @@
+package binarysearch;
+
+import lib.Printer;
+
+public class Problem1508_RangeSumOfSortedSubarraySums {
+
+    int B[];
+    public int rangeSum(int[] A, int n, int left, int right) {
+        B = new int[n+1];
+        for (int i = 0; i < n; i++) B[i+1] = B[i] + A[i];
+        return sum_k_sums(right) - sum_k_sums(left-1);
+    }
+
+    private int sum_k_sums(int k) {
+        int score = kth_score(k), res = 0, i;
+//        System.out.println(score);
+        for (int j = 1; j < B.length; j++) {
+            i = j-1;
+            while (i >= 0 && B[j]-B[i] <= score) {
+//                System.out.print(B[j]-B[i] + "  ");
+                res += B[j]-B[i];
+                i--;
+            }
+            if (i == j-1) break;
+        }
+        return res;
+    }
+
+    private int kth_score(int k) {
+        if (k == 0) return 0;
+        int lo = 1, hi = B[B.length-1];
+        while (lo < hi) {
+            int mi = lo + (hi-lo)/2;
+            if (count_sum_under(mi) < k) lo = mi+1;
+            else hi = mi;
+        }
+        return lo;
+    }
+
+    private int count_sum_under(int score) {
+        int res = 0;
+        for (int j = 1, i = 0; j < B.length; j++) {
+            while (B[j]-B[i] > score) i++;
+            if (i == j) break;
+            res += j-i;
+        }
+        return res;
+    }
+
+    public static void run() {
+        Problem1508_RangeSumOfSortedSubarraySums solution = new Problem1508_RangeSumOfSortedSubarraySums();
+        int A[] = {1,2,3,4}, n = 4, left = 1, right = 5;
+        int res = solution.rangeSum(A, n, left, right);
+        Printer.print(res);
+    }
+}