qselect example added

examples/qselect.imp

+# Quick-select, abstracted
+# Upper Bound: O(n)
+
+def qselect():
+    var lo, hi, p, pos, N
+
+    lo = 0
+    p = 0
+    hi = N - 1
+
+
+    while [lo >= 0 ] lo < hi:
+        tick(hi - lo)
+        p = rand(N)
+
+        if p = pos:
+            hi = lo
+        else:
+           if p < pos:
+              lo = p + 1
+           else:
+              hi = p - 1