93 lines
2.2 KiB
Go
93 lines
2.2 KiB
Go
package top100liked
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import (
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"fmt"
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"slices"
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"testing"
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)
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// https://leetcode.cn/problems/word-search/description/?envType=study-plan-v2&envId=top-100-liked
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func exist(board [][]byte, word string) bool {
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w := []byte(word)
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l := len(word)
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m := len(board)
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n := len(board[0])
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// 下、右、上、左
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move := [4][2]int{{1, 0}, {0, 1}, {-1, 0}, {0, -1}}
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// 减枝让耗时降低了很多
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var boardCnt [128]int // 覆盖 ASCII，字母在范围内
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for _, row := range board {
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for _, c := range row {
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boardCnt[c]++
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}
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}
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var wordCnt [128]int
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for _, c := range w {
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wordCnt[c]++
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}
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// 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。
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for _, char := range w {
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if boardCnt[char] < wordCnt[char] {
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return false
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}
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}
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// 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。
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if boardCnt[0] > boardCnt[len(boardCnt)-1] {
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slices.Reverse(w)
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}
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var helper func(idx, row, col int) bool
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helper = func(idx, row, col int) bool {
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for _, v := range move {
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new_row := row + v[0]
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new_col := col + v[1]
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if new_row >= 0 && new_row < m && new_col >= 0 && new_col < n && w[idx] == board[new_row][new_col] {
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if idx == l-1 {
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return true
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}
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board[new_row][new_col] = '#'
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if helper(idx+1, new_row, new_col) {
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return true
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}
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board[new_row][new_col] = w[idx]
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}
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}
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return false
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}
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for i, row := range board {
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for j, col := range row {
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if col == w[0] {
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if l == 1 {
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return true
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}
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board[i][j] = '#'
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if helper(1, i, j) {
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return true
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}
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board[i][j] = w[0]
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}
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}
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}
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return false
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}
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func Test(t *testing.T) {
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fmt.Printf("%+v\n", exist([][]byte{{'A', 'B', 'C', 'E'}, {'S', 'F', 'C', 'S'}, {'A', 'D', 'E', 'E'}}, "ABCCED"))
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}
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func Test2(t *testing.T) {
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fmt.Printf("%+v\n", exist([][]byte{{'A', 'B', 'C', 'E'}, {'S', 'F', 'C', 'S'}, {'A', 'D', 'E', 'E'}}, "SEE"))
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}
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func Test3(t *testing.T) {
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fmt.Printf("%+v\n", exist([][]byte{{'A', 'B', 'C', 'E'}, {'S', 'F', 'C', 'S'}, {'A', 'D', 'E', 'E'}}, "ABCB"))
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}
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