Bug fixes and improvements (#1348)

* Add "reference" for EN version. Bug fixes.

* Unify the figure reference as "the figure below" and "the figure above".
Bug fixes.

* Format the EN markdown files.

* Replace "" with <u></u> for EN version and bug fixes

* Fix biary_tree_dfs.png

* Fix biary_tree_dfs.png

* Fix zh-hant/biary_tree_dfs.png

* Fix heap_sort_step1.png

* Sync zh and zh-hant versions.

* Bug fixes

* Fix EN figures

* Bug fixes

* Fix the figure labels for EN version

zh-hant/codes/go/chapter_backtracking/n_queens.go

@@ -15,6 +15,7 @@ func backtrack(row, n int, state *[][]string, res *[][][]string, cols, diags1, d
 
 		}
 		*res = append(*res, newState)
+		return
 	}
 	// 走訪所有列
 	for col := 0; col < n; col++ {

zh-hant/codes/go/chapter_backtracking/permutations_ii.go

@@ -23,7 +23,7 @@ func backtrackII(state *[]int, choices *[]int, selected *[]bool, res *[][]int) {
 			(*selected)[i] = true
 			*state = append(*state, choice)
 			// 進行下一輪選擇
-			backtrackI(state, choices, selected, res)
+			backtrackII(state, choices, selected, res)
 			// 回退：撤銷選擇，恢復到之前的狀態
 			(*selected)[i] = false
 			*state = (*state)[:len(*state)-1]