feat: further improve sliding window search

Short exit when we already have the information we want

Author: scolladon

leetcode/binary-search/719-find-k-th-smallest-pair-distance.md

@@ -101,22 +101,25 @@ class Solution {
         int lo = 0, hi = nums[nums.length - 1] - nums[0];
         while (lo != hi) {
             int mi = lo + (hi - lo) / 2;
-            if (count(nums, mi) < k) lo = mi + 1;
+            if (isCountBelowThreshold(nums, mi, k)) lo = mi + 1;
             else hi = mi;
         }
         return lo;
     }
 
-    private int count(int[] nums, int d) {
+    private boolean isCountBelowThreshold(int[] nums, int d, int k) {
         int right = 1;
         int count = 0;
-        while (right < nums.length) {
-            int left = 0;
-            while (nums[right] - nums[left] > d) left++;
-            count += right - left;
-            right++;
+        int left = 0;
+        while (right < nums.length && count < k) {
+            if (nums[right] - nums[left] > d) { 
+                ++left;
+            } else { 
+                count += right - left;
+                ++right;
+            }
         }
-        return count;
+        return count < k;
     }
 }
 ```