u

2026-07-03 10:27:25 +08:00
parent 4850991edd
commit a01ef32bf7
4 changed files with 247 additions and 0 deletions
@@ -0,0 +1,92 @@
+package top100liked
+
+import (
+	"fmt"
+	"slices"
+	"testing"
+)
+
+// https://leetcode.cn/problems/word-search/description/?envType=study-plan-v2&envId=top-100-liked
+
+func exist(board [][]byte, word string) bool {
+	w := []byte(word)
+	l := len(word)
+	m := len(board)
+	n := len(board[0])
+	// 下、右、上、左
+	move := [4][2]int{{1, 0}, {0, 1}, {-1, 0}, {0, -1}}
+
+	// 减枝让耗时降低了很多
+
+	var boardCnt [128]int // 覆盖 ASCII，字母在范围内
+	for _, row := range board {
+		for _, c := range row {
+			boardCnt[c]++
+		}
+	}
+
+	var wordCnt [128]int
+	for _, c := range w {
+		wordCnt[c]++
+	}
+
+	// 字符频次可行性预检。 扫一遍 board 统计各字符计数，若 word 中某字符出现次数超过 board 上的数量，直接 return false。
+	for _, char := range w {
+		if boardCnt[char] < wordCnt[char] {
+			return false
+		}
+	}
+
+	// 词序翻转剪枝（算法层面最大收益）。 统计 board 中 word[0] 和 word[l-1] 的出现次数，若首字符比尾字符更常见，就把 word 反转后再搜——从稀有端开始DFS，能在更浅层就剪掉大量无效分支。
+	if boardCnt[0] > boardCnt[len(boardCnt)-1] {
+		slices.Reverse(w)
+	}
+
+	var helper func(idx, row, col int) bool
+	helper = func(idx, row, col int) bool {
+		for _, v := range move {
+			new_row := row + v[0]
+			new_col := col + v[1]
+			if new_row >= 0 && new_row < m && new_col >= 0 && new_col < n && w[idx] == board[new_row][new_col] {
+				if idx == l-1 {
+					return true
+				}
+				board[new_row][new_col] = '#'
+				if helper(idx+1, new_row, new_col) {
+					return true
+				}
+				board[new_row][new_col] = w[idx]
+			}
+		}
+		return false
+	}
+
+	for i, row := range board {
+		for j, col := range row {
+			if col == w[0] {
+				if l == 1 {
+					return true
+				}
+				board[i][j] = '#'
+				if helper(1, i, j) {
+					return true
+				}
+				board[i][j] = w[0]
+			}
+		}
+	}
+
+	return false
+}
+
+func Test(t *testing.T) {
+	fmt.Printf("%+v\n", exist([][]byte{{'A', 'B', 'C', 'E'}, {'S', 'F', 'C', 'S'}, {'A', 'D', 'E', 'E'}}, "ABCCED"))
+}
+
+func Test2(t *testing.T) {
+	fmt.Printf("%+v\n", exist([][]byte{{'A', 'B', 'C', 'E'}, {'S', 'F', 'C', 'S'}, {'A', 'D', 'E', 'E'}}, "SEE"))
+}
+
+func Test3(t *testing.T) {
+	fmt.Printf("%+v\n", exist([][]byte{{'A', 'B', 'C', 'E'}, {'S', 'F', 'C', 'S'}, {'A', 'D', 'E', 'E'}}, "ABCB"))
+}