基本搜尋方法——簡介(二)

程式碼：

/*
 d=3 a=96 b=-69 BCDE
  d=2 a=69 b=-96 FGHI
   d=1 a=96 b=-69 MLKJ
    eval=7
   -7(v) >= -69(b) ret
  7(v) >= -96(b) ret
 -7(v) >= -69(b) ret

7
*/
// https://www.xqbase.com/computer/search_intro2.htm
// https://www.xqbase.com/computer/search_intro3.htm
#include <stdio.h>
#include 
 
<vector>

struct { char* haizi; int v; } nodes[] = {
    { "BCDE" }, // A
    { "FGHI" }, // B
    { "" }, { "" },    { "" }, // CDE
    { "KJLM" },    // F 改這裡可以“排序”
    { "NO" }, // G
    { "" }, { "" }, // HI
    { "", 11 }, // J
    { "", 12 }, // K
    { "", 9 }, // L
    { "", 7 }, // M
    { "", 5 }, // N
    { ""
 
, 6 }, // O
};

std::vector<int> pstack;    // position stack

char* gen_moves() { return nodes[pstack.back()].haizi; }
void apply_move(char m) { pstack.push_back(m - 'A'); }
void undo_move() { pstack.pop_back(); }
int eval() { return nodes[pstack.back()].v; }
#define I do { for (int i = 0; i < 4 - d; i++) putchar(' '); } while (0)

int
 
 alpha_beta(int d, int a, int b) {
    if (d <= 0) { int v = eval(); I;printf("eval=%d\n", v); return v; }
    char*    moves = gen_moves();
    I;printf("d=%d a=%d b=%d %s\n", d, a, b, moves);
    for (char* p = moves; *p; p++) {
        apply_move(*p);
        int v = -alpha_beta(d - 1, -b, -a);
        undo_move();
        if (v >= b) { I;printf("%d(v) >= %d(b) ret\n", v, b); return v; }
        if (v > a) { I;printf("%d(v) > %d(a)", v, a); a = v; }
    }
    I;printf("ret %d\n", a); return a;
}

int main() {
    pstack.push_back(0);
    printf("%d\n", -alpha_beta(3, 96, -69));
    getchar(); return 0;
}

這就對了？改下節點F的子節點的順序試試？

基本搜尋方法——簡介(三) 解釋為什麼排序這一步是很重要的。

其實本文的原標題是“Alpha-Beta搜尋很簡單…………嗎？”，聳人聽聞騙下點選。:-)

Insertion sort is used when number of elements is small. It can also be useful when input array is almost sorted, only few elements are misplaced in complete big array.

https://www.geeksforgeeks.org/c-program-for-insertion-sort/