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115-Distinct-Subsequences.js
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115-Distinct-Subsequences.js
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//////////////////////////////////////////////////////////////////////////////
// 1D Dynamic Programming
// Time: O(n*m)
// Space: O(m)
//////////////////////////////////////////////////////////////////////////////
/**
* @param {string} s
* @param {string} t
* @return {number}
*/
function numDistinct(s, t) {
const sLen = s.length;
const tLen = t.length;
if (sLen < tLen) {
return 0;
}
const cache = new Array(tLen).fill(0);
for (let r = sLen - 1; r >= 0; --r) {
let prev = 1;
for (let c = tLen - 1; c >= 0; --c) {
const curr = cache[c];
if (s[r] === t[c]) {
cache[c] += prev;
}
prev = curr;
}
}
return cache[0];
}
//////////////////////////////////////////////////////////////////////////////
// 2D Dynamic Programming
// Time: O(n*m)
// Space: O(n*m)
//////////////////////////////////////////////////////////////////////////////
/**
* @param {string} s
* @param {string} t
* @return {number}
*/
function numDistinct(s, t) {
const sLen = s.length;
const tLen = t.length;
if (sLen < tLen) {
return 0;
}
const cache = new Array(sLen + 1).fill().map(() => new Array(tLen + 1));
cache[sLen].fill(0);
for (let r = 0; r <= sLen; ++r) {
cache[r][tLen] = 1;
}
for (let r = sLen - 1; r >= 0; --r) {
for (let c = tLen - 1; c >= 0; --c) {
cache[r][c] =
cache[r + 1][c] + (s[r] === t[c] ? cache[r + 1][c + 1] : 0);
}
}
return cache[0][0];
}
//////////////////////////////////////////////////////////////////////////////
// Depth First Search Recursion With Memoization
// Time: O(n*m)
// Space: O(n*m)
//////////////////////////////////////////////////////////////////////////////
/**
* @param {string} s
* @param {string} t
* @return {number}
*/
function numDistinct(s, t) {
const sLen = s.length;
const tLen = t.length;
if (sLen < tLen) {
return 0;
}
const cache = new Array(sLen).fill().map(() => new Array(tLen));
return countDistincts();
/**
* @param {number=} i = `0`
* @param {number=} j = `0`
* @return {number}
*/
function countDistincts(i = 0, j = 0) {
return j === tLen
? 1
: i === sLen
? 0
: cache[i][j] !== undefined
? cache[i][j]
: (cache[i][j] =
countDistincts(i + 1, j) +
(s[i] === t[j] ? countDistincts(i + 1, j + 1) : 0));
}
}