2021-06-07：一个字符串添加最少的字符变成回文串，回文串有多个，请返回所有结果。

package main

import (
    "fmt"
    "math/rand"
    "time"
)

func main() {

    rand.Seed(time.Now().Unix())
    TOTAL := 1000
    for i := 0; i < TOTAL; i++ {
        s := genRandString()
        ret := getPalindromeStringList(s)
        fmt.Println(i, s, ret)
    }

}

func genRandString() string {
    ans := make([]byte, rand.Intn(3)+3)
    for i := 0; i < len(ans); i++ {
        ans[i] = byte('A' + rand.Intn(26))
    }
    return string(ans)
}

func getPalindromeStringList(s string) []string {
    if len(s) == 0 {
        return []string{}
    }
    dp := getDp(s)
    N := len(s)
    M := N + dp[0][N-1]
    ansVal := make([]string, 0)
    ans := &ansVal
    path := make([]byte, M)
    process(s, dp, 0, N-1, path, 0, M-1, ans)
    return *ans
}

// 当前来到的动态规划中的格子，(L,R)
// path ....  [pl....pr] ....
func process(s string, dp [][]int, L int, R int, path []byte, pl int, pr int, ans *[]string) {
    if L >= R { // L > R  L==R
        if L == R {
            path[pl] = s[L]
        }
        *ans = append(*ans, string(path))
    } else {
        if dp[L][R-1] == dp[L][R]-1 {
            path[pl] = s[R]
            path[pr] = s[R]
            process(s, dp, L, R-1, path, pl+1, pr-1, ans)
        }
        if dp[L+1][R] == dp[L][R]-1 {
            path[pl] = s[L]
            path[pr] = s[L]
            process(s, dp, L+1, R, path, pl+1, pr-1, ans)
        }
        if s[L] == s[R] && (L == R-1 || dp[L+1][R-1] == dp[L][R]) {
            path[pl] = s[L]
            path[pr] = s[R]
            process(s, dp, L+1, R-1, path, pl+1, pr-1, ans)
        }
    }
}

func getDp(s string) [][]int {
    if len(s) == 0 {
        return [][]int{}
    }
    N := len(s)
    dp := make([][]int, N)
    for i := 0; i < N; i++ {
        dp[i] = make([]int, N)
    }
    //对角线以下无效
    //对角线默认全0
    //紧贴对角线的线，首尾相等为0，不等为1
    for i := 0; i < N-1; i++ {
        if s[i] != s[i+1] {
            dp[i][i+1] = 1
        }
    }

    //从下行往上行遍历，从左往右
    for i := N - 3; i >= 0; i-- {
        for j := i + 2; j < N; j++ {
            if s[i] == s[j] {
                //相等看【左下边】
                dp[i][j] = dp[i+1][j-1]
            } else {
                //不等看【左边】和【下边】
                dp[i][j] = getMin(dp[i+1][j], dp[i][j-1]) + 1
            }
        }
    }

    //二维dp表
    return dp
}

func getMin(a int, b int) int {
    if a < b {
        return a
    } else {
        return b
    }
}