tasks a-s

Task/N-queens-problem/Icon/n-queens-problem-1.icon

@@ -0,0 +1,16 @@
+procedure main()
+    write(q(1), " ", q(2), " ", q(3), " ", q(4), " ", q(5), " ", q(6), " ", q(7), " ", q(8))
+end
+
+procedure q(c)
+    static udiag, ddiag, row
+
+    initial {
+        udiag := list(15, 0)
+        ddiag := list(15, 0)
+        row := list(8, 0)
+    }
+
+    every 0 = row[r := 1 to 8] = ddiag[r + c - 1] = udiag[8 + r - c] do   # test if free
+        suspend row[r] <- ddiag[r + c - 1] <- udiag[8 + r - c] <- r       # place and yield
+end

Task/N-queens-problem/Icon/n-queens-problem-2.icon

@@ -0,0 +1,3 @@
+procedure main()
+    every write(q(1), " ", q(2), " ", q(3), " ", q(4), " ", q(5), " ", q(6), " ", q(7), " ", q(8))
+end

Task/N-queens-problem/Icon/n-queens-problem-3.icon

@@ -0,0 +1,35 @@
+global n, rw, dd, ud
+
+procedure main(args)
+    n := integer(args[1]) | 8
+    rw := list(n)
+    dd := list(2*n-1)
+    ud := list(2*n-1)
+    solvequeen(1)
+end
+
+procedure solvequeen(c)
+    if (c > n) then return show()
+    else suspend placequeen(c) & solvequeen(c+1)
+end
+
+procedure placequeen(c)
+    suspend (/rw[r := 1 to n] <- /dd[r+c-1] <- /ud[n+r-c] <- c)
+end
+
+procedure show()
+    static count, line, border
+    initial {
+        count := 0
+        line := repl("|   ",n) || "|"
+        border := repl("----",n) || "-"
+        }
+    write("solution: ", count+:=1)
+    write("  ", border)
+    every line[4*(!rw - 1) + 3] <- "Q" do {
+        write("  ", line)
+        write("  ", border)
+        }
+    write()
+    return      # Comment out to see all possible solutions
+end