HDOJ-2234（迭代DFS）

4*4的矩阵，数字范围是[1, 4]，直接用数字表示的话，需要用3个bit表示，3*16=48，不尴不尬的，所以可以用4个bit表示一个数字，虽然冗余了，但16进制表示上还是比3bit的好看些：

#include <cstdio>typedef unsigned long long ULL;ULL rowMask[4][4] = {0}, wholeRowMask[4] = {0};ULL colMask[4][4] = {0}, wholeColMask[4] = {0};/*0  1  2  34  5  6  78  9  10 1112 13 14 15*/void initMask(){    for(int i = 0; i < 4; ++i){        for(int j = 0; j < 4; ++j){            rowMask[i][j] = static_cast<ULL>(0x0F) << ((4*i+j) << 2);            wholeRowMask[i] |= rowMask[i][j];            colMask[i][j] = static_cast<ULL>(0x0F) << ((i+4*j) << 2);            wholeColMask[i] |= colMask[i][j];        }    }}inline bool rowSame(ULL state){    ULL tmp = state & wholeRowMask[0];    return tmp == (state & wholeRowMask[1]) >> 16 &&           tmp == (state & wholeRowMask[2]) >> 32 &&           tmp == (state & wholeRowMask[3]) >> 48 ;}inline bool colSame(ULL state){    ULL tmp = state & wholeColMask[0];    return tmp == (state & wholeColMask[1]) >> 4 &&           tmp == (state & wholeColMask[2]) >> 8 &&           tmp == (state & wholeColMask[3]) >> 12 ;}inline ULL rotateLeft(ULL state, int row){    ULL res = state & ~wholeRowMask[row];    res |= (rowMask[row][1] & state) >> 4;    res |= (rowMask[row][2] & state) >> 4;    res |= (rowMask[row][3] & state) >> 4;    res |= (rowMask[row][0] & state) << 12;    return res;}inline ULL rotateRight(ULL state, int row){    ULL res = state & ~wholeRowMask[row];    res |= (rowMask[row][0] & state) << 4;    res |= (rowMask[row][1] & state) << 4;    res |= (rowMask[row][2] & state) << 4;    res |= (rowMask[row][3] & state) >> 12;    return res;}inline ULL rotateUp(ULL state, int col){    ULL res = state & ~wholeColMask[col];    res |= (colMask[col][1] & state) >> 16;    res |= (colMask[col][2] & state) >> 16;    res |= (colMask[col][3] & state) >> 16;    res |= (colMask[col][0] & state) << 48;    return res;}inline ULL rotateDown(ULL state, int col){    ULL res = state & ~wholeColMask[col];    res |= (colMask[col][0] & state) << 16;    res |= (colMask[col][1] & state) << 16;    res |= (colMask[col][2] & state) << 16;    res |= (colMask[col][3] & state) >> 48;    return res;}bool dfs(ULL state, int steps){    if(steps == 0) return rowSame(state) || colSame(state);//try to rotate one row or one col    --steps;    for(int i = 0; i < 4; ++i){        if(dfs(rotateLeft(state, i), steps)) return true;        if(dfs(rotateRight(state, i), steps)) return true;        if(dfs(rotateUp(state, i), steps)) return true;        if(dfs(rotateDown(state, i), steps)) return true;    }    return false;}int main(){    int test, i, j, n, steps;    ULL state;    initMask();    for(scanf("%d", &test); test; --test){        state = 0;        for(i = 0; i < 4; ++i){            for(j = 0; j < 4; ++j){                scanf("%d", &n);                state |= static_cast<ULL>(n) << ((4*i+j) << 2);            }        }        for(steps = 0; steps < 6; ++steps){            if(dfs(state, steps)) break;        }        printf("%d\n", steps < 6 ? steps : -1);    }    return 0;}

实际上我们将矩阵的所有数字都减去1，则范围变为[0, 3]，则现在只需要用2个bit就可以表示一个数字了，2*16=32，刚好是一个int的长度：

#include <cstdio>typedef unsigned int UINT;UINT rowMask[4][4] = {0}, wholeRowMask[4] = {0};UINT colMask[4][4] = {0}, wholeColMask[4] = {0};/*0  1  2  34  5  6  78  9  10 1112 13 14 15*/void initMask(){    for(int i = 0; i < 4; ++i){        for(int j = 0; j < 4; ++j){            rowMask[i][j] = static_cast<UINT>(0x03) << ((4*i+j) << 1);            wholeRowMask[i] |= rowMask[i][j];            colMask[i][j] = static_cast<UINT>(0x03) << ((i+4*j) << 1);            wholeColMask[i] |= colMask[i][j];        }    }}inline bool rowSame(UINT state){    UINT tmp = state & wholeRowMask[0];    return tmp == (state & wholeRowMask[1]) >> 8 &&           tmp == (state & wholeRowMask[2]) >> 16 &&           tmp == (state & wholeRowMask[3]) >> 24 ;}inline bool colSame(UINT state){    UINT tmp = state & wholeColMask[0];    return tmp == (state & wholeColMask[1]) >> 2 &&           tmp == (state & wholeColMask[2]) >> 4 &&           tmp == (state & wholeColMask[3]) >> 6 ;}inline UINT rotateLeft(UINT state, int row){    UINT res = state & ~wholeRowMask[row];    res |= (rowMask[row][1] & state) >> 2;    res |= (rowMask[row][2] & state) >> 2;    res |= (rowMask[row][3] & state) >> 2;    res |= (rowMask[row][0] & state) << 6;    return res;}inline UINT rotateRight(UINT state, int row){    UINT res = state & ~wholeRowMask[row];    res |= (rowMask[row][0] & state) << 2;    res |= (rowMask[row][1] & state) << 2;    res |= (rowMask[row][2] & state) << 2;    res |= (rowMask[row][3] & state) >> 6;    return res;}inline UINT rotateUp(UINT state, int col){    UINT res = state & ~wholeColMask[col];    res |= (colMask[col][1] & state) >> 8;    res |= (colMask[col][2] & state) >> 8;    res |= (colMask[col][3] & state) >> 8;    res |= (colMask[col][0] & state) << 24;    return res;}inline UINT rotateDown(UINT state, int col){    UINT res = state & ~wholeColMask[col];    res |= (colMask[col][0] & state) << 8;    res |= (colMask[col][1] & state) << 8;    res |= (colMask[col][2] & state) << 8;    res |= (colMask[col][3] & state) >> 24;    return res;}bool dfs(UINT state, int steps){    if(steps == 0) return rowSame(state) || colSame(state);//try to rotate one row or one col    --steps;    for(int i = 0; i < 4; ++i){        if(dfs(rotateLeft(state, i), steps)) return true;        if(dfs(rotateRight(state, i), steps)) return true;        if(dfs(rotateUp(state, i), steps)) return true;        if(dfs(rotateDown(state, i), steps)) return true;    }    return false;}int main(){    int test, i, j, n, steps;    UINT state;    initMask();    for(scanf("%d", &test); test; --test){        state = 0;        for(i = 0; i < 4; ++i){            for(j = 0; j < 4; ++j){                scanf("%d", &n);                state |= static_cast<UINT>(n-1) << ((4*i+j) << 1);            }        }        for(steps = 0; steps < 6; ++steps){            if(dfs(state, steps)) break;        }        printf("%d\n", steps < 6 ? steps : -1);    }    return 0;}

可以看到速度快了一倍，可以估计CPU操纵int型的数据还是比long long快一倍呢，虽然硬件电路上64bit的寄存器进行位操作和32bit的寄存器进行位操作相差无几（因为并行）