Add 528_Random_Pick_with_Weight.java

Author: seanprashad

Design/528_Random_Pick_with_Weight.java

@@ -0,0 +1,30 @@
+class Solution {
+    int[] prefix;
+    int totalSum;
+
+    public Solution(int[] w) {
+        prefix = new int[w.length];
+
+        for (int i = 0; i < w.length; i++) {
+            totalSum += w[i];
+            prefix[i] = totalSum;
+        }
+    }
+
+    public int pickIndex() {
+        int low = 0, high = prefix.length - 1;
+        double target = totalSum * Math.random();
+
+        while (low < high) {
+            int mid = low + (high - low) / 2;
+
+            if (prefix[mid] < target) {
+                low = mid + 1;
+            } else {
+                high = mid;
+            }
+        }
+
+        return low;
+    }
+}