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"))
}