Add 1.12

sicp-ex-1.12.rkt

@@ -0,0 +1,33 @@
+; 1
+; 1 1
+; 1 2 1
+; 1 3 3 1
+; 1 4 6 4 1
+; . . . .
+; I am sure that I have chosen the worst possible way
+
+(define (pasc-step row col num curr-row curr-col)
+  (cond
+    ((or (< col 0) (> col row)) 0)
+    ((or (= col 1) (= col row)) 1)
+    ((= curr-row row) num)
+    ((or (= col 2) (= col (- row 1))) (- row 1))
+    ((or (> col 2) (< col (- row 1))) (pasc-step
+          row
+          col
+          (+ num (if (< curr-col col)
+              (pasc-step curr-row (+ curr-col 1) 1 2 2)
+              (pasc-step curr-row (- curr-col 1) 1 2 2)))
+          (+ curr-row 1)
+          (if (< curr-col col) (+ curr-col 1) curr-col)))))
+
+(define (locate-pasc row col)
+  (pasc-step row col 1 2 2))
+
+(locate-pasc 2 1)
+(locate-pasc 3 2)
+(locate-pasc 4 3)
+(locate-pasc 5 2)
+(locate-pasc 5 4)
+(locate-pasc 6 4)
+(locate-pasc 7 3)